It’s official – the UK’s hybrid collection of measures is here to stay

Recently, one of our readers wrote to his MP about the UK’s measurement muddle. He received a reply from the office of the Minister for Universities and Science, David Willetts MP, who has responsibility for measurement standards in the UK. This reply confirms that the Government has no plan to reduce the current mixture of units in common use in the UK or to promote a single system of measurement for all purposes.

Since the start of the UK’s metric changeover in the 1960s, the Government has always maintained that one day we will become a metric country. We now learn that this target has been put off to an indefinite time in the future, or perhaps never.

This is the reply to our reader’s MP from David Willetts MP:

“22 May 2014

UK Measurement System

Thank you for letter of 7 May 2014, concerning an enquiry from your constituent, about the UK measurement system.

The UK is already substantially metric. The only authorised usages of imperial units as  primary indications are those referred to in your letter – the mile, yard, foot, and inch for road traffic speed, signage and distance measurement and the pint for draught beer or cider and doorstep milk – together with the troy ounce for the sale of precious metals. Imperial units also may be used alongside metric units in dual labelling.

The Government supports a single system of units of measurement in principle, but recognises that many people in the UK prefer or are more familiar with imperial units. Therefore, the Government is committed to retaining the existing usages of imperial units for as long as consumers and businesses find it useful.

Road traffic speed and signage are matters for the Department for Transport. However, I understand that they have previously estimated that a change to metric would cost in the region of £700 million.

The Government has no plans for further metrication to end the few remaining primary uses of imperial units or to end their use in dual labelling. There is no significant demand from business or consumers for such change and the costs are likely to far outweigh any benefits.

I hope your constituent finds this information useful.”

Mr Willetts repeats the DfT estimate for changing speed limit and distance signs of about £1200 per sign, when recent research has shown this figure to be closer to £120 per sign. One can only suggest that if the case for retaining imperial road signs were stronger, the Government would not have to rely on this dubious estimate.

Even Mr Willetts is unable to resolve the conflict between the Government’s support for a single system of units of measurement and the DfT’s resolute opposition to metric speed and distance signs, resulting in the continued existence of about half a million imperial-only signs on UK roads. Consumers will, of course, find inches, feet, yards and miles on road signs useful when there is no alternative. But they may then prefer these pervasive, and consequently familiar, units in usages where there is a choice. And so the muddle continues.

Leaving this nonsense aside, what does this hybrid collection of measures advocated by Mr Willetts and adopted by default by the Government look like?

Here are some of the measures readers may have encountered recently on the street, in the media or at home:

Length               millimetre, inch, foot, yard, metre, kilometre, mile

Area                   square foot, square metre, acre

Volume              millilitre, pint, litre, imperial gallon (for mpg), cubic yard, cubic metre

Mass                  gram, pound, kilogram, stone, tonne

Pressure            millibar, pounds per square inch, bar

Temperature    °C, °F

Power                watt, kilowatt, BTU per hour

Energy               joule and kJ, calorie and kcal, kilowatt hour, therm

“Fine” says Mr Willetts. “Apart from road signs, let business or consumers decide. Let them demand changes if they want them.” An easy option for him and his colleagues – put off the difficult decisions, and hope the problems will go way.

But how does, for example, a child learning numbers and measurement at school select which unit to use when there is such a bewildering choice?

A recent publication¹ deals with the impact on maths education of the “few remaining primary uses of imperial units” and the measurement muddle that results from them. Metric Views will be returning in the future to the subject of education.

¹ “How big is an acre? No one knows.” Written and published by Alan Young in May 2014, and available from

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67 Responses to It’s official – the UK’s hybrid collection of measures is here to stay

  1. Rob says:

    Alan Young.
    Very well said, however until we can get politicians on side the situation will not change, maybe you can copy your post of 7/8/14 to MPs.

  2. CharlieP says:


    Perhaps it's nothing more than a mere coincidence then that as Australia was actively sweeping away other symbols associated with the UK (they replaced British citizenship with Australian, they dropped the Union Flag, they removed "British" from their passports, they replaced God Save the Queen as their national anthem, they chose green and red over red, white and blue as their national colours) they also decided to be rid of the British currency system and the British measurement system.


    I don't, and have never said I do, "prefer using imperial measurements". What I have said, and what I am proud to believe though is, that as Britain has already proven its credentials as metric system user and as a leading international trader, it should not be a priority for the government to attempt (carefully chosen word) to force the British public to use metric for other purposes. That loose apples are still bought (and even openly sold) by the pound nearly 50 years after the British government started the metrication push and more than 40 years after UK commerce and industry (hence the UK workforce) embraced the metric system is evidence that there is no need to even try it.


    I don't see why any unit of pricing needs to be "primary". Consumers should be given the information they desire, whether it be Euros per litre, GBPs per gallon or whatever. In the same way that cash machines give the customer a language choice, petrol pumps could give currency/unit choice - and why not?

  3. CharlieP says:


    I once had similarly unenlightened views, but about languages. I thought children whose parents spoke different languages were at a distinct disadvantage, and I simply could not understand why British children had to study languages at school and why Esperanto wasn't used everywhere. However, as I matured, I quickly realised my mistakes. Now I'd give almost anything to have a second "native tongue".

  4. John Steele says:

    Charlie P

    I'm looking in as an outsider, but the Empire is dead. Australia achieved its independence in gradual steps with the concurrence of the UK. Its flag, like many British overseas possessions and Commonwealth nations has a Union Jack in its canton (upper left quadrant) and devices of local significance in the remainder of the field. (The design was approved in 1902 by King Edward VII.) It seems to me that such a flag takes much greater note of British heritage than flags of Canada, South Africa, and flags of about 2/3 of Commonwealth nations which seem to avoid such signs of heritage entirely.

    With the exception of mostly some Caribbean islands, the UK has fallen substantially behind most of its former Empire in metrication. (Not that the US has anything to brag about with respect to metrication)

  5. Erithacus says:

    A propos of the claim that people should be encouraged to use whatever measurement system they like, I thought the exchange below might be of interest. The incompetence, ignorance and lack of understanding speak for themselves. This is a typical product of 40 years of allowing two systems to co-exist, with no attempt at Government leadership.

    "The service available at Currys and PC World

    Dear Customer,

    Thank you for the recent email regarding the specifications for our freezers. I am sorry that I could not contact you today.

    I apologise for the inconvenience this has caused, the reason we use cu ft is because this is how the manufacturer measures the item during manufacture of the item.

    I can advise that 28.32litres = 1 cu ft and 1 litre = 3ft. I trust this will help in any future workings for any appliance.

    Kind regards,

    Wendy Doyle
    The KNOWHOW™ Team

    How did I do? Leave your feedback here:"

    "----- Original Message -----

    I have given up trying to use your website to buy a freezer as your
    filters are in "cu ft" but the specifications for the freezers are in
    litres. Isn't it time you moved into the 21st century and standardised
    on litres?"

  6. John Frewen-Lord says:


    Well they got the conversion from litres to cu ft right, but "I can advise ... 1 litre = 3ft." makes no sense.

    The KNOWHOW™ Team is more like The DON'TKNOWHOW™ Team.

    What manufacturer is still specifying refrigerators in cu ft?

  7. BrianAC says:

    As some would say "nothing wrong with using two systems of measurement". The problem arises when that someone does not understand either system.
    One thing I did learn at school as it was drummed into us "READ THE QUESTION", make sure you understand it before trying to answer. The point made was having all the fridge/freezers in litres and the search in cu ft right beside them, not unusual and more than a little confusing.
    I am confused about the 1 litre = 3ft bit, I thought this was a typo for 1metre, but that does not arise. Can it really be that stupid?
    As a side line I did a few fridge freezer searches and Currys seem to be worst at this, Amazon have a 9.5 cu ft fridge freezer with a shipping weight of 5 kg (another common error).

  8. jackthesmilingblack says:

    Have you noticed how passenger car specifications give interior volume in litres rather that cubic metres? Unless of course the spec. is in Imperial, in which case it's cubic feet. It does seem awfully unlikely that a future owner would be planning to fill the interior of his new vehicle with water, although I have to admit that 1,000 litres is a more impressive than one cubic metre. Further, the conversion between cubic feet and cubic metres can be a minefield for the unwary.
    Jack, the Japan Alps Brit

  9. Erithacus says:

    I don't agree with Jack about reserving litres for liquids. A litre is just an alternative name for a cubic decimetre (accepted by BIPM for use with SI). Thus it is a measure of capacity or volume - whether of liquid, gas or solids - or indeed empty space. I would guess that most people would find it easier to visualise, say, 237 L, rather than 0.237 m³, as the capacity of a fridge or car boot or whatever.

  10. jackthesmilingblack says:

    Splitting hairs, but the volume of a litre is a function of temperature and pressure, thus inviting the question, "A litre of what?"

    Editor. The litre is defined as one cubic decimetre exactly. The idea of defining weight using water occupying a certain volume led to many complications so we should be glad it is now history - blame John Wilkins (1614-1672) for suggesting it in the first place.
    This troubled relationship between the definition of volume and the weight of water will be the subject of a future article on MV.

  11. Michael Glass says:

    Charlie, the British also got rid of the British currency system and replaced it with a decimal currency, just as Australians and New Zealanders did. The Australian national colours are green and gold, the colours of our golden wattle.

    The notion that Australia and New Zealand adopted the metric system to spite the British is anachronistic and really quite dotty. Australian interest in changing to the metric system was so overwhelming that a senate committee's recommendation to change was unanimous. When this decision was made (1968 and 1970) the UK had already announced that it would switch to the metric system (1965). Australia could not afford to be the last one to hang on to the old system so there was a sense of urgency in metricating as it was expected that the United States would also change.

    As it happened, metrication hardly happened in the United States and it stalled in the United Kingdom. This, however, is not the fault of Australians and New Zealanders.

    I understand that you regret the growth of Australian independence, but it had nothing to do with the decision to metricate. You were the ones who decided to change before we did.

  12. John Steele says:


    The notion "but the volume of a litre is a function of temperature and pressure" is incorrect, but there is some confusing terminology that might be the cause of thinking this is true.

    Phrases like normal cubic meter (or liter), standard cubic feet etc., refer not to a real volume that a liquid or gas would occupy but the idealized volume it would occupy at some standardized pressure and temperature. The volume correction tables for petroleum products give a similar impression. However, it is the gas or liquid that is expanding and contracting. I'd like to say the container isn't, but in fact, but in fact it has its own temperature coefficient, usually much smaller. Containers used as provers are only rated to be correct at a specified temperature. A correction factor may be offered for temperatures near the specification.

    However, the volume of a space at the moment is determined by its dimensions at the moment, and the liter is just a special name for a cubic decimeter. Cubic feet may always be converted to liters by multiply by (3.048 dm/ft)³ and recognizing that 1 L = 1 dm³. However, if the cubic feet and liters are qualified by phrases like "normal" or "standard", the reference pressures and temperatures may be different and conversion becomes a minefield for the unwary. For petroleum products, the difference between 15 °C and 60 °F is considered significant for the precision expected in large commercial transactions (the volumes measured in either set of units are pretty debatable compared to the 5 decimal VCFs used). The problem must be separated into units conversion and standard condition adjustments, or tremendous confusion results.

  13. Percy says:

    All government policies will have to pass a "family test", David Cameron is expected to say in a speech later today the following: "Put simply that means every single domestic policy that government comes up with will be examined for its impact on the family." [ ]

    Does this include the Government's policy on metrication? Its failure to complete metrication etc.

    Consider: unite families, use the same units in the home, school, workplace, environment, - in fact everywhere!

    And ... 'Health issues, both physical and mental, are expected to be at the forefront of the new push.'

    So don't consider this Metric Views comment to be a 'red herring' - because eventually with an enormous amount of luck and with tonnes of optimism we might even get a shedding in the use of 'calories' when referring to food energy ...
    [ ]

  14. Ezra Steinberg says:

    Here is an excellent article that discusses a new book published about the rise and fall of the metric system in the USA:

    The article makes the point that Thomas Jefferson was the first person to introduce decimal currency (making the UK quite the latecomer to that party ;-). Jefferson was also convinced that the USA would adopt the metric system after France did during the Revolution. (The USA has in turn been much the latecomer to that party, alas .... and we are still waiting. 🙁

    Nonetheless, the author of the article does conclude with this hopeful note:

    "In America, however, repeated efforts at metrication, from Jefferson to Jimmy Carter, were scuttled by a formidable combination of hostility and indifference. According to Marciano the debate is now over since the digital revolution has made conversion instantaneous and a change of system pointless. Still, as his book beautifully shows, clashes over the meter were more often about ideology, not utility. And so, as long as the struggle continues over reason and faith, universalism and tradition, I wouldn’t count the meter out."

  15. CHRIS ANDREWS says:

    The only country in the world now not to have a metric currency is still as far as I am aware is MAURITANIA. As I have said elsewhere metrication in certain areas is fine, but surely in others why shouldn't imperial be used.

  16. derekp says:

    Alan Young, aka Dr Metric, reported as follows earlier today:


    Yesterday I attended BETT, an exhibition for all those interested in educational technology. I knew that Nicky Morgan, the Secretary of State for Education was giving the keynote speech, so I arrived with a pack for her which included three copies of my document ‘How Big is an Acre? No–one Knows’ and a covering letter. The place was so full and noisy that is was not easy to get to her, but I did manage to manoeuvre myself directly in front of her as she left the stage.

    I quickly explained that I had studied this problem for forty five years and this was probably going to be the only time in my whole life when I would be able to put my correspondence directly into the hand of a government minister. She seemed to see the funny side, accepted my package and promised to read my document personally.

    In addition, I also managed to speak to Sarah Montague of the BBC Radio 4 Today programme and gave her a copy of the document. She said John Humphreys would be very interested in it and said she would give him the copy. I have since sent further copies and my contact details.

    I’ll let you know if there are any further developments.

    A great day!"

  17. derekp says:

    A report by Louise Brooke-Smith, President of the RICS, on her visit to New York in February 2015 included the following:

    “A lunch hosted by Mike Bloomberg, the former NYC Mayor, saw an eclectic mix of media, arts, financial and tech professionals. Prior to this, a reception saw Boris Johnson and the UK Consul General, Danny Lopez, emphasise the importance STEM (Science, Technology, Engineering, Mathematics) subjects for economic progress. This theme was echoed at the high level EY panel discussing Foreign Direct Investment (FDI). This included the message that world class talent needs to be secured if huge skills gaps are to be addressed.”

    So, much talk about STEM but no talk about that important obstacle to the promotion of STEM subjects: the metric/customary measurement muddle that exists on both sides of the Atlantic.


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