300 million gallons and other dam(n) measurement units

In 2019, readers could be forgiven for having no idea what 300 million gallons of water looks like.

In a recent BBC news article about the Toddbrook Reservoir in Derbyshire, it was reported that, following storm damage, the dam was in danger of collapse with the potential of releasing 300 million gallons of water onto the nearby town of Whaley Bridge.


In 2019, readers could be forgiven for having no idea what 300 million gallons of water looks like.

To visualise large volumes it is often useful to calculate the length of a side of a cube with an equivalent volume.

Using imperial units, this is something that has always been difficult to do, due to the fact that liquid volumes are traditionally measured in units that don’t relate easily to length units. For example, in this instance we would want to know how many cubic feet, or cubic yards, there are in 300 million gallons. Without knowing the conversion factor for gallons to cubic feet, this would require the use of a search engine and calculator. We would also need to make an assumption as to which gallon is being used. Is it the imperial gallon which hasn’t been used for trade for at least 30 years, or is it the US gallon, which is sometimes reported in parentheses for American readers.

If we are given the value in metric units (litres or cubic metres), the exercise is straight forward, and requires practically no arithmetic. Converting litres (cubic decimetres) to cubic metres is simply a matter of dividing by 1000. A cubic metre is quite easy to visualise and is the standard unit used on all water utility bills.

The volume of water is approximately 1.3 million cubic metres. For visualisation purposes, we can approximate this to a cube of 1 million cubic metres. Such a cube has a side of length 100 metres, or one hectometre. Therefore, with little effort, it is possible to visualise the enormous volume of water reported as being slightly more than one cubic hectometre, or a cube with a side as long as a 100 metre running track.

The report continues, and mixes units when it quotes the metric units being used by the emergency services: The fire services are quoted as “pumping out 7,000 litres of water a minute”, in a bid to bring down the water level, and the police were quoted as having plans for scenarios including the dam collapsing “which holds back 1.3 million tonnes of water”.

At the time of writing, the emergency services are still in a race against time to prevent further deterioration of the dam from more heavy rain. We wish everyone involved well.

36 thoughts on “300 million gallons and other dam(n) measurement units”

  1. One tonne of water has volume of a cubic metre, so knowing that the the dam holds 1.3 million tonnes of water also tells us that it’s capacity is 1.3 million cubic metres.


  2. Probably just as disappointing is that today, Monday 5th, they are still converting rainfall in inches, and decimal inches at that!


  3. In the US, many towns were built along a 6 mile x 6 mile grid called a township, which easily approximates to 10 km x 10 km (100 km^2) or 10 000 m x 10 000 m (100 000 000 m^2). 1 300 000 m^3 (0.0013 km^3) of water divided into 100 000 000 m^2 would 13/1000 or 13 mm of water depth. The city I live in is about 10 km x 10 km in area. This is how I would imagine this water volume to be. It would cover my town in 13 mm of water, assuming of course, the entire town were perfectly flat, which it isn’t.

    It isn’t very deep once it settles, but the major damage would come from the inrush as 0.013 km^3 of water comes gushing out all at once.


  4. The BBCs use of outmoded metrology seems to contradict the first two edicts of its royal charter to ‘inform, educate and entertain’. Very few people accurately understand measures in decimal inches or decimal miles but the BBC keeps on trotting them out. How many tape measures are graduated in tenths and how many people know how many metres, feet or yards there are in three tenths of a mile without using a calculator? It’s not informative OR educational to offer the public something obscure when a simpler and more precise form exists.
    I doubt that more than 5% of the population know what an acre is, other than a way estate agents and the media describe land, but hectares, which have been taught at schools for fifty years, and are the legal units of measure, are still passed over by the BBC in preference to the more obscure unit.
    If I remember correctly, gallons were replaced at the petrol pump in the UK in the late eighties and I can’t think of anything else other than fuel that people would still buy or sell in gallons in the twenty first century. It’s a little like the BBC using shillings and pence to describe financial transactions. At least they don’t do that.
    Sadly, and as perverse as it seems, I think the main reason the BBC dumbs down with customary measurements is to try to compete with the popular media which seems to think that anything not emanating from the USA is elitist and ‘uncool’.
    The BBC should not drop its principles to appease that sort of wooly-minded thinking but it will continue to do so until it’s challenged. Unfortunately I can’t see any politicians or influential members of the public doing anything as enlightened as that right now.


  5. As we can probably guess, all these conversions are done automatically with some form of auto-inkorrecting software. It would seem that high volumes of water are converted to gallons. This was so on BBC (300 mgall) and ITV (286 mgall) TV news, I think all the others did similar.
    This is probably the same auto-inkorrecting software that changes degrees Celsius to F’s without knowing the context, not to mention the ‘First Letter Capitalisation’ responsible for changing kg to Kg, and removing the second capital in other units which is even more annoying.
    I think we have our eyes on the wrong targets with this issue.

    Maybe rather dubiously I can claim to be one of the 5% of people in the whole world that ‘understands’ acres, miles, yerds, chains, furlongs, cwt, stones and even Lsd, now is that not a wonderful feeling (not)?


  6. Just saw a BBC news report on the impeachment of Trump and the connections to Ukraine. Sadly, all the distances were given in “miles” (not even “kilometers” added).

    Sad commentary both on the BBC and on the failure of the government to convert road signs back in the sixties when it had the chance. 😦


  7. If the BBC is broadcast world-wide, then kilometres should be used. Unless, the editors, reporters, commentators, etc want deliberately force the world to hear and thus force them to understand imperial/USC units. In this way they hope that as long as the proverbial foot is stuck in the door, there is always hope of a complete reversion to pre-metric units.

    The cost to keep miles on the roads is ongoing and adds up to higher figures year after year and long ago exceeded the cost of replacement. The cost comes into play when instruments for sale in England have to be produced in miles for the English market and kilometres for the world-wide market. England also drives on the left like Ireland and cars made for Ireland use a metric display and for England a mile display. Second hand metric displayed vehicles imported to England have to be switched to mile displays at a cost. The auto shop doing the conversion however does make a nice profit.


  8. WHICH? magazine.
    Cliff’s reference to GALLONS AT THE PETROL PUMP …[ above, 2019-08-06 ]
    In the latest survey by Which? magazine .. the best car etc.
    [invitations to take part now – with the results to be published later this year] …
    it uses miles per gallon!
    It is yet another extremely sad and annoying example of this ‘Consumer Protection Organisation’ failing to promote metrication.


  9. @Fred –
    No surprises there then!
    One of the worst examples we have in this country.


  10. Perhaps mpl as a compromise, given the presence of litres but not km on the road network.


  11. If it’s illegal to sell fuel or anything else by the Imperial gallon, how is it permissible to use ‘miles per (illegal) gallon’ to indicate vehicle performance?


  12. @Jonn Smith

    Just checked the Ford Canada web site and see that the new fully electric Mustang has its range given in kilometers only and the gasoline powered vehicles have their range given in L/100 km (only).

    Yet another data point showing how converting road signs to metric (which Canada did back in the 70’s) makes the change-over to metric in the mind of the general public essentially irreversible.


  13. We must try to adopt symbols, and get away from abbreviations.
    mph and kph are abbreviations.
    Of course m/L is not acceptable ..
    [unless metres per litre is a meaningful physical quantity – which I don’t think it is!]
    Sorry John, I don’t support your idea/compromise.


  14. @Andy ah well, in that case zero progress, but at least ideological purity wins.


  15. @Jake a quick google has shown that labeling is covered by EU Directive 1999/94/EC (updated by Statutory Instruments (SI) 2004 No. 1661; 2013 No. 65; and 2018 No. 673 (published June 2018)).

    Following this particular rabbit hole leads us to The Passenger Car (Fuel Consumption and CO2 Emissions Information) Regulations 2001 and within that you find in Schedule One REQUIREMENTS FOR THE FUEL ECONOMY GUIDE in paragraph 2 therein;

    ..Fuel consumption shall be expressed either in litres per 100 kilometres (1/100km) or kilometres per litre (km/l), and quoted to one decimal place, or, to the extent compatible with the provisions of Council Directive 80/181/EEC(1) in miles per gallon…

    Following that Council Directive leads us to Council Directive of 20 December 1979 on the approximation of the laws of the Member States relating to units of measurement and on the repeal of Directive 71/354/EEC (80/181/EEC), which I think is the source of the UK opt outs with respect to Imperial measures.

    I think, as it is a bit of a maze.


  16. @ John Smith

    Thank you for doing that research. I see that certain Imperial units are defined in metric terms in 80/181/EEC and are allowed to be used in certain contexts. But for me it still defies logic for the ‘gallon’ to be unlawful for the sale of petrol and diesel but lawful, indeed required, for the expression of the fuel economy achieved with that same fuel. Most drivers will never have bought a ‘gallon’ of fuel in their life (trips to the USA not withstanding, but that’s a different gallon again). Is there not a point at which common sense has to kick in?


  17. @Jake well it took, what nearly 50 years for dual metric imperial height restriction signs to be introduced, so I’d say give it another 50 years before mpg goes – wouldn’t want to rush things would we lol


  18. @Ezra,Jake

    Or as I put it elsewhere, are we expecting too much of the human race?


  19. So, what’s up (again) with the BBC? I thought “acres” (at least) had been chucked into the dustbin of history. See the video below at the 53 second (or so) mark:


    While things certainly are bad in East Africa (another climate crisis instance, alas), the BBC does not help by using the obsolete unit “acre”. I thought even the British government had tossed that unit out in favor of “hectares”.

    Can someone please clarify what the status (both official and actual) is of the unit “acre” is these days in the UK?


  20. Ezra,

    How many times do you need to be told the reason? The BBC may have a policy on units but doesn’t enforce them nor will. A specific reporter or editor will use their preferred units and not care if their their units are universal or not. So, when you see a reporter using non-metric units, that is because it is their personal preference or the preference of their editor. They hope the whole world by encountering their use of non-metric units will force themselves to learn and be familiar with these units. Their hope is the reader/listener will begin to like the non-metric units, become comfortable using them and even promote them.

    So, the next time you encounter someone using these units just tell yourself they are promoting their personal choice or the choice of their editor.


  21. Jake said: “If it’s illegal to sell fuel or anything else by the Imperial gallon, how is it permissible to use ‘miles per (illegal) gallon’ to indicate vehicle performance?”

    Jake, the reason is that it may be illegal to sell by the gallon, but it is not illegal to use gallons or any other non-related units in advertising as that interferes with the free speech rights. Also buying fuel in litres and converting to gallons to calculate fuel consumption adds an extra step and a possible error in the calculated result that it is meant to discourage the average driver from bothering to do the calculation.

    I also think that the people who most often talk about fuel consumption are the same people hung up on tyre rim sizes, personal body measurements and TV screens in non-metric units. That is those in metric related discussion groups. These are items at the fringe of normal conscious thinking. What is gained by always calculating fuel consumption only to get the same results each time? If the results change, what can be done? Nothing. So, why bother calculating? The figure may only come into play when buying a car and how often is that? Once every 10 years?

    The same is true with other rare occurrences of non-metric units. How often does TV screen sizes, personal dimensions and tyre rims come up in conversations or are on people’s minds when they do their daily/weekly shopping? How often is one in the market for a TV or a tyre rim? The last few times I bought tyres for the car, the rim size never came up. The tyre salesman used a scanner device to scan my car’s barcode for the VIN number, opened up a screen on his computer monitor and showed me all of the tyres, prices, warranties, etc available for my car and I made a choice. Not once were inches mentioned. But, all the tyre sizes available were from the p=metric series.

    The point is these remnant uses of non-metric units appear solely in fringe areas and never in the mainstream.


  22. @ Ezra Steinberg, who wrote: Can someone please clarify what the status (both official and actual) is of the unit “acre” is these days in the UK?

    Ezra, I believe the acre became obsolete once all land registration moved over to metres and hectares. So for that reason alone the national broadcaster, the BBC, should take note of that fact and stop using it.


  23. Jake,

    Read my response to Ezra and you will understand why there will be no note taking and using the acre and other imperial units will continue. The opposition does not recognise the abolishment of the acre.


  24. So, I apologize for the repetition, but is there any way to flog the BBC into submission?

    Why my frustration? The BBC service that calls itself the WORLD SERVICE (my emphasis) had a report today from a Kenyan (clear from his accent) talking about the number of ACRES (my emphasis) eaten up so far by a massive plague of locusts in that country and neighboring countries in East Africa.

    Obvious question: why would a Kenyan, who gets this information from his government in hectares, think to a convert that information to Imperial? And why would the BBC so-called “World Service” (my quotation marks) not remind that poor, lost soul that “acres” are no longer an accepted unit in the UK (let alone the rest of the world aside from the USA)?

    Time for a few pints down at the local pub (if there were one here!) to drown my sorrows, eh, mates? 😦


  25. @ Daniel Jackson

    Whether specific groups (‘opposition’) recognise the demise of the ‘acre’ is neither here nor there. The media should simply not be allowed to use units of measurement that are not in legal use any longer. I mean, we don’t see or read about prices in ‘shillings and pence’ any more, except in a historical context, so why should the media be using measurements that are in the same category as phased-out coinage. Freedom of speech is fine and dandy, but the media aren’t doing anyone any favours.


  26. Ezra & Jake,

    It isn’t just the BBC. Here starting at 0:42 in the video the commentator for this DW news report mentions a swarm of locusts 60 km long by 40 km wide destroying hundreds of thousands of acres instead of thousands of square kilometres.

    Even though the size of the swarm given in kilometres shows an exact measurement, the value given in acres is vague. Why acres and not square kilometres? Did the BBC give an exact number of acres or was it the same as here, a vague figure? Forest fire damage in the US is often given in the US in millions of acres instead of square kilometres or some other four-letter word. Why?

    Could it be the resulting number of acres compared to square kilometres is meant to give a higher more impressive sounding number? Did the government of Kenya use hectares or is that an assumption? Maybe they gave square kilometres. The swarm of 60 km x 40 km results in an area of 2400 km^2 or 240 000 hectares. The figure in acres would be 2.5 times this. Whether hectares of acres both are in the hundreds and thousands.

    Here is an AP article that uses round kilometres with not-so round miles in parentheses:


    Here is a New York Post article that copies the AP article but in one paragraph drops the kilometres and in the rest of the article keeps them:


    No mention of acres at all. I think the media like to use acres over square kilometres in the same way the media likes to use horsepoopers over kilowatts. They can inundate the ignorant with huge numbers meant to sound impressive. The epitomé of fake news. The ignorant informing the ignorant, the blind leading the blind.

    The real issue is not using hectares instead of acres, its in not using square kilometres.


  27. Jake said: “Freedom of speech is fine and dandy, but the media aren’t doing anyone any favours.”

    The news reporters and editors are not trying to do any favours, that is not their intent. Their intent is to inundate the masses with their personal preferences and hope they force the listener/reader to adopt their ways instead of the standards. This is why the media is so full of fake news. It goes beyond using dead measuring units. A lot of what is said or written is more often exaggerated or simply untrue. Cleaning up bad unit usage is only part of the problem.

    The first step to correct this problem would be for reporters and editors to be tried and given fines and jail time if what they report is not verifiable true. This would curb a lot of the fake news emanating from news services.


  28. @ Daniel Jackson

    You’re taking a wider view than I am, and you’re probably right. Another bugbear of mine in UK news is to describe an area as so-many football fields. We have had humorous references over the years to the use of well-known landmarks, buses and other typically British things to refer to the height or size of something, but the football field is in a class of its own. It assumes you actually know how big a football field is and visualise things in terms of them. News travels across borders and into other languages, of course. I have heard the ‘football field’ reference in the news of other non-English-speaking European countries, probably because the idea has been carried over. I think this is very retrograde. It’s a form of contamination.


  29. As a long-time technical writer I can complain about the news articles (especially the BBC) just from an editing standpoint as well. The total unruly mishmash of units (sometimes Imperial, sometimes metric, sometimes both with metric first, sometimes both with Imperial first, sometimes with erroneous conversions) would leave any decent editor shaking his or her head in utter disbelief and chagrin!

    As has been said before, using straight up metric would help readers from both perspectives. Maybe someday? (Hope springs eternal.)


  30. Jake,

    It may be that the reporters/editors in trying to push imperial on the population are meeting with some interesting resistance. The resistance is taking the form of reduced readership rather than the readers trying to learn imperial in order to understand. A number of on-line British news services seem as of late to be constantly asking for donations to keep going, something that wouldn’t happen if readership was up.

    So rather than concede and use the units the world understands they push for a compromise in describing distances in football fields, buses and other such things and by doing so the metric reader is to interprets that to a fixed number of metres and the imperial reader to a fixed number of yards. Hopefully this can only end if enough of the metric readership shuns the media until metric is used fully or the media’s bottom line suffers to the point they either force the use of metric or go out of business. Either way it becomes metric or nothing at all.


  31. Ezra,

    The only effective means of complaint is for you to actively boycott the offending institutions and pass the word to others to do the same.


  32. @Jake, football fields and other damn measures!

    I wanted to refrain from this, but a day or two ago a new ‘low’ was reached on TV media.

    The ‘anti-Brexit’ flag to be draped over the white cliffs of Dover is the size of two squash courts.

    Well, I have no idea what ‘quash’ is, let alone the size of a squash court!!!
    Please do not tell me, I really have less than no interest.


  33. Brian, the official squash court regulations are in metric:


    Those squash court specifications are designed to ensure that equal playing conditions are provided for tournaments around the world. These squash court specifications clearly outline the size of the court (9,75m in length, 6,4m in width and 5,64m in height, measured from the top of the parquet floor). The playing surfaces permitted (no more than two different wall surfaces), the amount of light recommended (500 Lux) and even the amount of times, the air in the squash court should be exchanged per hour (four times).

    Since the “flag ” is the size of two, the media didn’t tell you how the two were laid relative to each other.


  34. For a bit of a change of pace I thought I would report something positive, namely “The Economist” videos on YouTube.

    This is a recent report about the use and mis-use of planting trees to offset carbon emissions into the atmosphere (which I found very well done and informative):

    I noticed that all of the units used are metric, such as degrees Celsius, hectares, and square kilometers. No mention of Imperial anywhere. What a joy! (And all of the videos from The Economist as best I remember do the same and stick to just metric.)

    Too bad that so-called world-renowned British news service cannot see fit to do the same. Very sad, indeed. 😦


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