Acres made easy

We look ahead to the 400th anniversary of an innovation that simplified the measurement of land area, initially in England and later in the UK, by introducing decimals.

Today when we measure land area the calculation is straightforward. Consider a minimum sized football pitch, defined as 90 x 45 metres or 100 x 50 yards.

In metric, area = 90 x 45 = 4050 sq m = 0.405 hectare.

In Imperial, area = 100 x 50 = 5000 sq yards = 5000/4840 acre.

Dividing by 4840 is simple, so long as you have a calculator or smart phone to hand. It was less so four centuries ago, before the arrival of electronic and mechanical calculators, the slide rule and logarithms.

Step forward English clergyman and mathematician Edmund Gunter, 1581–1626, who developed a chain, 22 yards long with 100 links. Ten of his chains made a furlong, which, like the rod and the acre, had enjoyed legal recognition since the late thirteenth century. A furlong was 40 rods, and one acre was equal to 160 square rods, or using Gunter’s system ten square chains, hence 100 000 square links.

Back to our modern football pitch. Using Gunter’s chain, the pitch would measure about 4 chains 54 links (4.54 chains or 454 links) by 2 chains 27 links (2.27 chains or 227 links).

Area = 454 x 227 = 103 058 sq links = 1.03 acres.

Gunter’s chain, which he introduced in 1620, became extremely popular. Railway surveyors and engineers in the 19th century used Gunter’s chain for setting out – much of the line from London to Reading, constructed in the 1830s, is at a gradient of 1/1320 or 1 foot in 20 chains. Readers who use British railways may also have noticed markers on bridges and other structures, for example “91 m 56 ch”. And the length of a cricket pitch is, of course, one chain.

When sorting through my dad’s tool box a few years ago, I came across a “modern” equivalent of Gunter’s chain – a linen tape. A link is 7.92 inches, as this photo illusrates.

Gunters tape

When we think of pioneers in the simplification of England’s arcane measures, a name that comes to mind is John Wilkins, 1614-1672, first Secretary of the Royal Society, who proposed a decimal system. But his proposal was never followed up in England whereas Gunter’s innovation was quickly adopted. It dramatically simplified the calculation of land area, and survived well into the twentieth century until overtaken by technological developments and the UK’s metric changeover.


11 thoughts on “Acres made easy”

  1. When a lot of countries metricated, they kept some of the unit names and recycled them to rounded metric values. The chain is one of those units whose name can be recycled unofficially to 20 m. Thus the with it equal to 100 links, each link is 200 mm. Ten chains to a furlong becomes 200 m, and a rod being 1/40-th of a furlong would be exactly 5 m. An acre being 160 square rods would be 160 x 5 x 5 or 4000 m^2. A quarter acre lot would be 1000 m^2 and a mile would be exactly 1600 m.

    The area of a football field would then be 4050/4000 or slightly over 1 acre, an exact value not being important.

    All of these units except the mile are deprecated and have no legal status, so they can easily be turned into non-official units with rounded metric values, such that they can be measured with a metric tape measure or other metric calibrated device. Those with a cultural hangup can continue to speak these terms but to everyone else, it would be simple mental arithmetic to put them into proper metric perspective.


  2. Daniel Jackson:

    That’s an interesting post about countries metricating and recycling old unit names to rounded metric values. I must say, I do not know many of examples of where this has happened and I’m sure where it has happened it has been the general public, rather than surveyors or other professionals, who have let the old names live on as metric units. ‘Pound’ in various European languages to mean 500 grams comes to mind. I have certainly heard that usage. But I have my doubts as to whether your ideas for old imperial names being recast as metric units would either catch on or be very practical. I think it would be more confusing than helpful. Better to jettison the old once and for all time and simply adapt to the new. It has largely been done in Britain already. It’s just a question of getting those pesky ‘supplementary indicators’ dropped once and for all and getting the road signs upgraded and switched completely to match what children actually learn in school. It really is a betrayal of their education that this has not happened already.


  3. Jake,

    A number of units names have been recycled. But just to make it perfectly clear, these units would be illegal as any form of trade unit. They would just be used by those still clinging to old units due to comfort with the names. This way the rest of us could move forward and they can have an easy reference to their old names.

    The Ottoman Dunam is another recycled unit name. It varied all over the place, but is today it is the same as the decare or 1000 m^2.

    Chinese traditional unit names have all been recycled to mean a round metric value. The jin or catty has the same value of the pound at 500 g and is legally weighed out on a metric scale, just like the pound.

    As much as we would like to see people give up these units for modern SI units, it isn’t going to happen quickly. It takes generations. By recycling the unit names it allows for a de-legalisation of them in trade and a softening of resistance to metrication. How much better would it be for shoppers still clinging to the word pound if in the UK it was decided that all shops would be required to weigh out 500 g to every request for a pound? Resistance to full metrication comes mostly from those that have difficulty converting metric pricing to “old money” with weird conversion factors. They aren’t going to give up and just go metric, they are just going to resist all the more.

    The other countries knew that in order to make metrication go easy and smooth, they had to allow people who are comfortable with the old names to be able to continue to use the names with some sort of comfort.


  4. Martin,

    You are 100 % correct, but not everyone is in agreement with that view and they are resisting. There are those older people who are comfortable with the “old money” and no amount of preaching is going persuade them otherwise. The reason there is an outcry among this group for a return to imperial is because they can’t and won’t relate to impossible to work with conversion factors.

    If you tell them that as of a certain date that a all market pounds will hence forth mean 500 g, and show them half of the kilogram pricing and 5 times the 100 g pricing is pound pricing, they calculate easily any price or amount in old money and would become less resistant to metric only scales and pricing. Grant it some will complain until the last day, but the majority will adjust. It worked elsewhere, it will work in the UK.


  5. Daniel Jackson wrote: “As much as we would like to see people give up these units for modern SI units, it isn’t going to happen quickly. It takes generations.”

    I’m sorry but I don’t really agree with this. There is a precedent in the UK with the switch to decimal currency in 1971, which I remember very well. It was well planned, the public were properly informed and it was smoothly executed. The non-decimal coins were quickly withdrawn from circulation, so it was not possible to ‘take your pick’ of which system of coinage you preferred to use. That is the root of the present measurement muddle: metric has been introduced in many areas, but in many other, highly visible areas such as road signs, imperial has been left. I cannot imagine for one moment imagine that a British government would have embarked on the original changeover plan if it had known the mess we would end up in. It doesn’t take generations to change. I would say the present generation of older people would adapt very quickly. Everyone has experienced metric measures in the shops, filling up the car, buying soft furnishings, etc. The units are not alien and are taught in school. Many people are familiar with metric on road signs from travel around Europe or further afield. And, very importantly, I would venture to say that older people today are better educated than they were fifty years ago and would find no problem at all in adapting very quickly to metric on the roads. The only thing stopping this from happening, as far as I can see, is the DfT and the imperial vigilantes.


  6. I think they should recycle the lb = 500 g, same with a pint – make it 500 ml. Then the imperial nuts will be happy, well maybe not the ones that drink beer.


  7. @Jake is spot on, I would say.

    As I have mentioned previously, the example of conversion of road signs in Ireland and thus the conversion of everyday conversation to metric in just a matter of a few years demonstrates how quickly completion of metrication in the UK could happen if the government had the will to make it so by converting road signs there as well.

    Even Canada, which is bombarded massively every day with American movies, television, newspapers, etc. converted thermostats, weather reports, and road signs to metric decades ago; those folks have consistently stuck with metric when it comes to distances, speeds, temperature, barometric pressure, etc. despite the “Imperial” onslaught from the USA. (A common remark I hear from Canadians is “I have no idea what Fahrenheit temperatures mean.” or “We don’t understand ‘miles’ or ‘miles per hour’.”)

    The Canadian experience belies any suggestion that it would take a long time to get everyday folks thinking in and using metric day in and day out provided the government simply does what is necessary to help make it happen.


  8. Surely the persistence of the use of ‘livre’ in France undermines Jake and Ezra’s argument. That is an example where an historic measurement of weight has been adjusted to the metric system and is still widely used.
    It seems to me that one of the few arguments that the opponents of the metric system can muster is a cultural one. The old measurements are part of our culture and permeate our literature. Do we really want to stop people ‘going out for a pint’. Allowing old-style units to persist in a metricated form, where possible, undermines the cultural argument.
    However, it could not happen informally without a lot of arguments in shops and pubs. It needs the Government to declare that from a certain date the word ‘pound’ will be taken to mean 500g and the word ‘pint’ 500ml as Martin and Dawei suggest.


  9. David Tittle wrote: “It needs the Government to declare that from a certain date the word ‘pound’ will be taken to mean 500g and the word ‘pint’ 500ml as Martin and Dawei suggest.”

    As far as I am aware, ‘livre’ and its equivalents in other European languages do not have any legal status. They are simply ‘understood’ to mean 500 grams now. Given that, I cannot see any need for the British government to legislate to change the meaning of the word ‘pound’ or ‘pint’ in law. While no one in their right mind would complain if they were given 500 g instead of the ‘pound’ of 454 g, the Luddites might well still complain if their ‘pint’ were served as a half litre, which would simply aggravate bar staff. Better to legislate for the proper metric units and let names follow if customers wish to use them. I do know of a precedent for this: many Irish-themed bars around continental Europe, which are required to serve in metric units, have price lists showing, for example, ‘Pint Guinness 50 cl’, and you are served half a litre. That arguably keeps the cultural idea alive and complies with the law.


  10. It really doesn’t matter one way or the other if the French use the word livre for 500g. In Australia it’s half a kilo or 500g. As for culture, forget this nonsense! Culture changes. Language changes. Culture doesn’t need to be preserved in aspic.


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