A metric time line for the UK

Metric Views has attempted to produce a timeline showing progress in the British Isles towards the adoption of a single, simple, rational and coherent measurement system. This article takes the story up to 1980 – the events of the past thirty years will be the subject of a further post later. Readers’ suggestions for additions and amendments are welcome.

AD 43 – 412
Britain is occupied by the Romans and adopts Roman measures. These are common throughout much of Western Europe, the Balkans, Romania, the Middle East and North Africa, and include the Roman pound and mile (the latter being ‘mille passus’ or 1000 passus – one passus is two paces of a Roman legionary).

412 – 1066
Anglo-Saxon and Danish England. New measures appear alongside those of the Romans, for example for length:
1 digit (base of long finger), about 2 cm
10 digits = 1 small span (span of thumb and forefinger)
10 small spans = 1 fathom (1 arm-stretch from finger tip to finger tip), about 2 m
10 fathoms = 1 chain
10 chains = 1 furlong
10 furlongs = 1 thus-hund or one thousand fathoms, about 2000 m

1066 onwards
The Normans bring continental measures such as the ounce. The measurement muddle gets worse.

Magna Carta says “Let there be one measure …”  However, enforcement in medieval times is sometimes poor, and this clause in Magna Carta should be seen as an indication of a problem but not foreshadowing a solution.

1400 onwards
A ‘rough and ready’ decimal system is used increasingly for navigation at sea:
100 fathoms = 1 cable
10 cables = 1 nautical mile (approximately one minute of arc of latitude along a meridian)
1 knot = 1 nautical mile/hour

1642 – 1659
Civil war and revolution in England.
John Wilkins, born in Oxford and a student and graduate of the University, becomes Warden of Wadham College in 1648. He is joined by a number of experimental scientists, including Robert Boyle and Robert Hooke, who during the 1650s make Wadham one of the leading scientific institutions of Europe.

Restoration of the Monarchy. Wilkins loses his posts at Oxford.
In November, twelve experimental scientists, some from the Oxford ‘college’ and including Boyle, Isaac Newton and Wilkins meet in London to hear a lecture by Christopher Wren. Wilkins chairs the meeting, which agrees to form a scientific society with him as secretary.

King Charles II becomes patron of the society which is renamed The Royal Society. Hooke is appointed curator of experiments.

Wilkins, now Dean of Ripon and FRS, publishes a theory of everything entitled “An essay towards a real character and a philosophical language”. It is likely that many of his ideas were formulated during discussions with colleagues at Oxford and London. They include proposals for a new simplified measurement system with key features that will be incorporated in the metric system over a century later:
* a universal standard of length,
* a simple relationship between length and volume (or capacity),
* a simple relationship between length and weight or mass,
* units increasing by a factor of 10.

Newton becomes President of The Royal Society, and sets about undermining the reputation of rivals, in particular Hooke. Wilkins’ work is largely forgotten.

The Kingdom of Great Britain is formed by the Act of Union of England (and Wales) and Scotland. The Act achieves uniformity of measures by imposing those of England on Scotland.

1761 onwards
The opening of the Bridgewater Canal gives rise to a boom in canal construction. The Ramsden chain comprising 100 links each of one foot is adopted by engineers seeking accuracy with simplicity. (Author’s note. Ramsden chains were still around in the 1960s – we used one during a practical surveying course that I attended in 1963.)

1761 and 1769
The need for observations of the two transits of Venus results in a burst of unprecedented international scientific cooperation, with Britain taking a leading role. Will this continue for the world’s next great scientific endeavour – the development of a modern and internationally accepted measurement system?

James Watt tries to compare the results of his experiments on steam power with those from other countries. He writes to Irish chemist Richard Kirwan FRS: “I had a great deal of trouble in reducing the weights and measures to speak the same language; and many of the German experiments become still more difficult from their using different weights …” He also writes to Joseph Priestley FRS, and fellow member of Birmingham’s Lunar Society, asking him to encourage the scientists of England and France to cooperate to set up a common decimal system of weights and measures. Thanks to Kirwan’s international connections and Priestley’s contacts, Watt’s views are made known to Talleyrand and Lavoisier, both of whom play key roles in the creation of the metric system a few years later.

On 5 February, Sir John Riggs-Miller, MP for Newport, Cornwall, proposes in the House of Commons the reform of the English customary system of weights and measures in favour of a scientifically founded system. A proposal from France suggesting collaboration on this project is rejected by the British Foreign Secretary. Riggs-Miller loses his seat in Parliament at the general election later that year.

Sir Benjamin Thompson, Count Rumford, FRS, suggests that heat can be derived from motion (or mechanical energy), rather than, as was believed at the time, being a property of matter.

The UK is created by the Act of Union of Great Britain and Ireland. Irish measures are unaffected, but pressure on the Government to simplify the UK’s measurement muddle increases.

A Royal Commission is appointed to consider more uniform weights and measures. In their first report, the Commissioners agree that a uniformity of weights and measures is obviously desirable. It finally recommends simplifying English customary measures rather than using the metric system, at that time adopted only by The Netherlands including Belgium and Luxembourg.

The proposals of the Commission are the basis of the Weights and Measures Act 1824 and of the Imperial system that follows from it. This Act establishes standards for the primary units and ‘tidies up’ arcane laws without radically changing the multiplicity of customary weights and measures used throughout the country. Indeed, it expressly states that “it shall [be] lawful [to] buy and sell goods and merchandize (sic) by any weights or measures established either by local custom or founded on special Agreement” provided their exact relation to the standard units defined by the Act was generally known.
The USA retain English customary measures.

James Prescott Joule, a Manchester brewer and physicist, publishes a paper proving the equivalence of thermal and mechanical energy and endorsing the work of Rumford almost fifty years earlier. (Recognising this, SI has one unit for both heat and mechanical energy, the joule; Imperial has difficulty accommodating Rumford’s discovery and has two units, the British thermal unit and the foot-pound.)

The Great Exhibition draws attention to the advantages of a common international system of measurement.

Joseph Whitworth (of screw thread fame) proposes a decimal measure of length for mechanical engineering, and the ‘thou’ is added to engineers’ vocabulary.
A British branch is formed of the International Association for Obtaining a Uniform Decimal System of Measures, Weights and Coins.

1861 – 62
The application of the metric system in the fields of electricity and magnetism is developed through the British Association for the Advancement of Science (BAAS), under the active leadership of two British scientists, J C Maxwell and William Thompson, later Lord Kelvin. The BAAS insists that electrical units should coherent with the metric system and that electrical and mechanical energy should have the same unit, and proposes additional metric prefixes micro and mega.

A Select Committee of Parliament recommends that the use of the metric system should be made legal but that “no compulsory measures should be resorted to until they are sanctioned by the general conviction of the public.”

The Weights and Measures (Metric System) Act permits the use of metric measures but has little practical impact on industry or commerce.

A committee of the BAAS recommends using the CGS (centimetre-gram-second) system of units, and makes proposals for electrical units. The CGS system becomes the basis for scientific teaching and research for the next seventy years; however it includes two systems of electrical units, electromagnetic and electrostatic, which limits its practical use.

The UK sends a delegate to the conference that establishes The Metre Convention, but is not one of the original seventeen signatories.

The British firm Johnson, Matthey & Co secures an agreement with the French Government to supply thirty standard metres and forty standard kilograms.

The United Kingdom becomes a signatory of The Metre Convention and joins the General Conference on Weights and Measures (CGPM).

One of each of the standard metres and standard kilograms that had been cast by Johnson, Matthey & Co are selected at random as the reference standard, and the other standards, having been cross-correlated with each other, are distributed to the signatory nations of The Metre Convention.

The first practical international set of electrical units is proposed.

A second Weights and Measures (Metric System) Act permits the use of the metric system for all purposes in the UK. Like the 1864 Act, this Act has little practical effect.

The adoption of the metric system in British workshops is proposed at the International Engineering Congress in Glasgow. It is said that, “from time to time, orders have been lost for hardware and textiles, owing to manufacturers not troubling to make them in the standards of other countries.”

The House of Lords debates metrication and votes to make metric compulsory after two years. The House of Commons fails to rise to the challenge.

The Olympic Games are held in London. Track and field events take place at a new purpose-built stadium at White City. The Official Report says, “The introduction of the metric system is an innovation which may have proved some little inconvenience to British runners.”

The UK Met Office follows the lead of the International Meteorological Organisation (forerunner of the World Meteorological Organisation) and adopts the millimetre as the official standard unit of rainfall measurement.

The British Broadcasting Company Ltd is set up by six telecommunications companies. It begins transmitting public broadcasts from London using amplitude modulation of waves of constant frequency (and length). Radio sets that enable listeners to tune to a range of stations are calibrated by wavelength in metres. For some Britons, this is their first encounter with metric measures.
Twenty-six Irish counties leave the UK.

1936 – 38
The Ordnance Survey adopts a kilometre-based national grid for all mapping of Britain.

The Olympic Games return to London, centred on Wembley.
At a meeting of representatives of Canada, the UK and the USA held in November at the National Bureau of Standards, Washington, it is agreed that the three countries would make the unified thread their first choice. This is a screw thread system introduced for defence equipment (1939-44), in which the thread form and pitch are a compromise between British Standard Whitworth and American Standard Sellers.

The Committee on Weights and Measures Legislation (the Hodgson Committee) concludes that metric conversion is inevitable, and that the long-term advantages which would flow from an organised change would far outweigh the inconveniences of the change itself (Department for Transport please note). It adds that, prior to the metric change, the currency should be decimalised.

The Prime Minister, Harold Macmillan, opens the M6 Preston Bypass, Britain’s first motorway. This has metric distance posts at 100 metre intervals beside the hard shoulder.
Representatives from Australia, Canada, New Zealand, South Africa, the UK and the USA meet to discuss the possible adoption of a common definition for the inch, and thus the other imperial/USC units for length. A compromise value of exactly 25.4 mm is agreed, to take effect in 1959.

A Joint Committee appointed by the BAAS and the British Chambers of Commerce notes the world trend towards the metric system but finds insufficient support in British industry for making the change. In its report entitled, “Decimal currency and the metric system: should Britain change?” it concludes that there would be a 10 to 20 percent saving in mathematics teaching and a five percent overall saving in teaching time for children aged 7 to 11 years from the change.

The CGPM, including delegates from the UK, approves an updated version of the metric system, renamed the International System of Units (SI).
India, one of the UK’s largest export markets, announces that it will switch from Imperial to metric.

The Met Office switches internally from Fahrenheit to Celsius. This had been adopted by the World Meteorological Organisation as the standard unit for temperature measurement.

The Met Office adds temperatures in degrees Celsius to weather forecasts (it initially uses the obsolete term centigrade).
The British Standards Institution (BSI) issues a statement, “Change to the metric system?”, setting out the main issues, and this is widely circulated in industry for comment.
The final report of the Molony Committee on Consumer Protection states, “A uniform system of weights and measures, nationally used and enforced, is plainly part of the basic vocabulary of consumer protection.”

In October, BSI publishes “British industry and the metric system”, summarising the results of its consultation with industry. This shows that a large majority is firmly in favour of starting a change to the metric system without delay and without waiting for the rest of the Commonwealth and the United States. The report concludes that there is a unanimous desire for decision and that indecision was “acting as a curb to industrial progress”.
The Weights and Measures Act ends reliance on national physical standards for imperial measures of length and mass and introduces the following definitions:
1 yard = 0.9144 metre,
1 pound = 0.453 592 37 kg.
(For capacity, the 1824 definition of the gallon as the volume of ten pounds of water does not change, although it is linked to the metric system as a result of the redefinition of the pound and the inch.)

In February, the President of the Federation of British Industries (now the CBI) tells Ministers that the majority of its members are in favour of the adoption of metric as the primary measurement system.
In May, in response to a parliamentary question, the Government announces that they “… consider it desirable that British industries on a broadening front should adopt metric units sector by sector, until that system can become in time the primary system of weights and measures for the country as a whole …” and that “the Government hope that within ten years the greater part of the country’s industry will have affected the change.”
In November, major sectors of British industry approve a policy statement that urges British firms to regard the traditional screw thread systems – Whitworth, BA and BSF – as obsolescent, and to make internationally-agreed ISO metric thread as their first choice (with the ISO Inch (unified) thread as second choice) for all future designs.

The BSI and the Ministry of Technology issue Handbook 18, “Metric standards for engineering”, to be applied to all products that will be exported to Common Market countries.
A Parliamentary Standing Committee on Metrication is appointed.

BSI publishes a report, PD 6245 “Going metric – first stages”, setting out the background to the change, how standards will be provided, how the change should be programmed and the role of Government. It also suggests that SI, rather than metric technical units, is the logical system for the UK.
The education system starts moving to metric units following the publication of guidance by the Department of Education and Science (DES).
The agreed timetable for the metric changeover in the construction industry is published.
International paper sizes begin to replace old favourites such as foolscap, quarto and letter.
The UK Hydrographic Office begins a programme of modernisation of nautical charts and conversion of depth readings into metres – the scales of charts are already decimal.

Following a conference of editors of journals relating to science and technology, The Royal Society publishes agreed recommendations. These are that SI should be used in journals in preference to Imperial, CGS or metric technical units, and that the changeover should be made as quickly as possible.
The BSI publishes policy document 6424, “The adoption of the metric system in engineering: Basic programme and guide”.
The DES arranges several conferences to consider the consequences moves in the education system towards metric units.
In July, the setting up of a UK Metrication Board is announced.

1969 – 75
The building and construction industries progressively adopt SI, beginning with dimensional co-ordination, product development and then project design, finally moving on to construction on site.

From 3 March, the metric system becomes obligatory for the dispensing of prescriptions; bottled medicines are accompanied by 5 mL spoons.
On 28 May, the Metrication Board holds its first meeting under the chairmanship of scientist and broadcaster Lord Ritchie Calder. Its task is to facilitate the UK’s transition to the metric system. Its first report “Going metric: first five years, 1965-69” begins with the words, “Britain will be a metric country before 1975.”
Examinations for students starting higher education courses in science, engineering or technology are set in SI units.

The Government agrees to fund the redrafting of over 2000 British Standards in metric terms.
There is a change of Government, and in October the House of Commons debates metrication.
In December, the Minister for Transport Industries is asked in Parliament “if he will state the estimated cost involved in alterations to vehicles and road signs of all kinds if metric distance and speed measurements are introduced into this country.” He replies, “Nearly £2 million for speed limit signs: the Government have however decided that speed limits will not be made metric in 1973 and have no other date in mind.”
The Commonwealth Games adopt the metric system for all events.

Decimal currency is introduced on 15 February.

The White Paper on Metrication (Cmnd. 4880) confirms that metric units should become the primary system of measurement in the UK, and says that the changeover should take place in a well-ordered and regulated manner.
The Building Regulations are reissued in metric units to match progress in the building industry.

Education in primary schools is now in metric – science has been taught in metric since the turn of the century.
The Ordnance Survey begins the publication of 1:50,000 map sheets replacing the One Inch Seventh Series, and effectively ending the ‘Battle of the scales’ that had begun in the eighteenth century.
Metric measurements are given on clothing labels.
The International Rugby Football Board announces that from 1975 all measurements in the game will be metric, for example the 25 yard line will become the 22 metre line and the 5 yard line will become the 5 metre line.

The Royal Mail changes to metric measures for postal tariffs.
Tea, sugar, milk, soft drinks and other essentials begin to appear in rational (‘hard’) metric packaging in grocers and supermarkets.
Other voluntary retail initiatives include the pricing of floor covering and carpet in metric.

Speedometers on all new vehicles are required to be marked in mph and km/h.
A major carpet retailer (now no longer in business) finds enormous commercial advantage in reverting to sales by the square yard because these prices appear to customers to be 20% cheaper than those in metric. Metrication of carpet sales enters into a full-scale reverse. It is realised, belatedly, that a voluntary approach to the retail changeover does not work. Retail associations press the government for cut-off dates for imperial pricing of a wide range of products.

The furlong, cubic yard, bushel and dram cease to be legally authorised.
The Government delay seeking Parliamentary approval for further orders relating to metrication. It would not be until 1994 that these orders would finally be approved.

There is a change of Government, and on 14 November the new Consumer Affairs Minister announces that the Metrication Board will be dissolved on 30 April 1980 and that further metrication should be “on a voluntary basis”.

The square inch, square mile, cubic inch, cubic foot, hundredweight, ton, horsepower and Fahrenheit cease to be legally authorised.
The UK Metrication Board is abolished. The Government say that “metrication has now been extensively adopted in manufacturing industry and also in retail trade, where most packaged goods sold in prescribed quantities are now sold in metric sizes, so there is now very limited scope for the Board’s activities, …”
The metric transition stalls.

At that time, it could hardly have been foreseen that arguments would continue and the transition to metric measures drag on for a further twenty years (and still counting).

In the final part of the UK metric time line, to be posted in the future, we shall see increasing European co-operation highlighted when the Airbus A380 enters service, the impact of globalisation with three Japanese volume car manufacturers setting up metric production lines in Britain, the imperial gallon redefined in metric terms, renewed political controversy and of course erratic progress with the metric transition.

(Author’s note.
Thanks to all those who made suggestions with a view to improving the time line. These will be incorporated before it is copied to the UKMA web site. DP. 2012-06-15)

9 thoughts on “A metric time line for the UK”

  1. *1965
    In November, major sectors of British industry approve a policy statement that urges British firms to regard the traditional screw thread systems – Whitworth, BA and BSF – as obsolescent, and to make internationally-agreed ISO metric thread as their first choice (with the ISO Inch (unified) thread as second choice) for all future designs.*

    I have read this in other places also, but I am sure an earlier step is being missed out, but I don’t have the reliable knowledge to qualify that. In spite of all this, (or because of it) the government of the day decided AGAINST this and instead opted for the unified thread system (the Atlantic bridge again) and those awful ‘8-32′ and ’10-24’ screws. I remember the charge hand of the then Marconi Wireless Telegraph Company workshop (http://news.bbc.co.uk/1/hi/business/4375106.stm) being beside himself with rage over this, stomping up and down the workshop saying ‘we have to go metric sometime, this just adds to the cost for industry, we re-stock now, and we have to re-stock again in a few years time’. How very true this was. Anyone working on cars of the 1950’s to 1980’s will know of the change from BSF/Whitworth to UNF in 1960, then eventually to Metric (the mini Metro) I don’t know when, probably the 1965 switch, just 5 years and the entire UK industry re-tooling, re-stocking and re-designing everything twice. Now remind us again how much not going fully metric is costing us. Tell us again how much it would cost to go fully metric. Alas, still lessons cannot be learnt. Let’s get this awful fiasco behind us once and for all, but I fear not in my lifetime.

    Oh, and a bit of ammo for the other side, industry would have to re-tool every few years anyway so what’s the problem? Well, a lot of difference between scheduled replacement and forced compliance replacement.


  2. The UK was not formed in 1707. The Kingdom of Great Britain was. The UK is the United Kingdoms of Great Britain and Ireland a hundred years later.


  3. Derekp

    Interesting timeline. I would like to suggest two areas for possible revision.

    1959: Per NiST SP 447, the conference that produced the compromise value 25.4 mm/in was actually in 1958, with the value to take effect in 1959. The conference also included national lab directors of Australia, Canada, New Zealand, and South Africa, and the compromise value was apparently suggested by Canada. I think it is at least worth noting the other four countries party to the agreement.

    1873: The CGS system had a long period of use in physics; however, the electrical units included both esu and emu units and were not widely used for very long. A “practical international” set of electrical units was first proposed in 1893 and refined in 1908. While poorly realized, they agree within about 0.05% or better with modern electrical units. Giorgi first proposed a rationalized coherent system by adding the ohm to the meter-kilogram-second system in 1901. The fourth unit was later changed to the ampere, and the MKSA system was formally adopted by the IEC in 1935 and the CIPM in 1946. This was an immediate precursor to the SI, adopted in 1960.

    I do not feel equipped to write the required additional entries from a British perspective, but you may find the following summary helpful:


  4. Royal Society still uses calories
    In their 1972 report on nutritional sciences, the Royal Society identified the problem of the continued use of calories to describe energy content of food.
    “We recommend that editors of journals should not allow the use of the word ‘calorie’ …”
    See Metric Views : http://metricviews.org.uk/2010/03/joules-on-the-menu-please/

    BUT, the Royal Society still uses calories; in 2002 it published “The health hazards of depleted uranium munitions Part II” (ISBN 0 85403 5745), in a Conclusion it stated ‘Children consume more calories per kilogram of body weight than adults…’
    See: http://royalsociety.org/uploadedFiles/Royal_Society_Content/policy/publications/2002/9954.pdf (page 72)

    The Royal Society should be actively helping to complete metrication in the UK and when it means food energy it shouldn’t use the word ‘calories’.

    There are other Royal Society documents that still use ‘calories’ these include:
    ‘Report of Royal Society policy seminar on the scientific understanding of obesity’
    [RS Policy Doc: 03/06]; and in April this year published ‘People and the planet’
    a quote “… lifestyle and an increased calorie intake is leading to an increase in the average …… per capita supply of calories has remained almost stable in …”
    See: http://royalsociety.org/uploadedFiles/Royal_Society_Content/policy/projects/people-planet/2012-04-25-PeoplePlanet.pdf


  5. The Met Office’s web site has some interesting dates to add to the metrication timeline:

    Click to access Fact_sheet_No._9.pdf

    “The Met Office uses the millimetre as the official measurement of rainfall. This was adopted by the International Meteorological Organisation (forerunner of the WMO) as the standard unit of rainfall measurement and formally adopted by the Met Office on 1 May 1914.”

    “The scale of temperature used by the Met Office for measuring air temperature is Celsius. This was adopted by the World Meteorological Organisation as the standard unit of temperature measurement and formally adopted by the Met Office on 1 January 1961.”


  6. Some more notable pre-1980 events …

    “Decimal coinage and the metric system: Should Britain change?”, a joint report by the British Association for the Advancement of Science and the Association of British Chambers of Commerce, concludes that there would be a 10–20 percent saving in mathematics teaching and a 5 percent total teaching time saving, for those aged between 7 and 11 years, from a move to the metric system.

    1962 July 25
    The final Report of the Molony Committee on Consumer Protection states, “A uniform system of weights and measures, nationally used and enforced, is plainly part of the basic vocabulary of consumer protection.”
    (Cmnd. 1781, July 1962)

    1965 May 24
    “the Government consider it desirable that British industries on a broadening front should adopt metric units, sector by sector, until that system can become in time the primary system of weights and measures for the country as a whole.”
    “the Government hope that within ten years the greater part of the country’s industry will have effected the change.”

    1966 March
    The Parliamentary Standing Joint Committee on Metrication is appointed.

    1968 July 26
    Setting up of the Metrication Board is announced.

    1970 October 27
    Metrication is debated in the House Of Commons.

    Metric measurements added to clothing labels.

    1977 January 1
    Speedometers on all new vehicles are required to be marked both in km/h and in mph (miles per hour).
    http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:31975L0443:EN:HTML (Annex II 4.4.2)

    1979 November 14
    Sally Oppenheim, Consumer Affairs Minister, announces that the Metrication Board will end on 30 April 1980, and that further metrication should be “on a voluntary basis”.


  7. Many sports that weren’t already metric converted to metric measurements in the 20th century. Some chose soft metric conversions such as tennis and soccer, whereas others such as rugby chose to redefine measurements in rational metric values.

    Here are a couple of sport-related dates to add to the metrication timeline:

    The Commonwealth Games goes all metric.

    1974 May 17
    The International Rugby Football Board announces that from 1975 all measurements in the game will be metric. The old 25-yard line becomes today’s 22-metre line. The old 5-yard line becomes the 5-metre line.


  8. Some of the dates mentioned in the article (and comments) give pause for thought, and really make you realise how progress has slowed in my lifetime (despite being assured by teachers that everything would be metric by the time I left school (I’m still waiting)).

    * 75 years (give or take) since Ordnance Survey adopted metric measures for the national grid.
    * 50 years since the Met Office switched to celsius in weather forecasts
    * but perhaps most surprising, almost 100 years since the Met Office started to measure rainfall in mm, but yet still the BBC often refers to rainfall in “inches” and flooding in “feet”, which must be a real insult to the meteorologists and members of the emergency services who provide the source data in standard measurements..


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