An unnatural foot

Ronnie Cohen looks at the tenuous link between the imperial foot and human feet.

Imperial defenders often claim that imperial units are more “natural” and human in scale than metric units. It is true that human body parts have been the basis of many early forms of measurement (e.g. distance of elbow to finger tip for the cubit, width of most people’s hands for the hand – a unit used for measuring the height of horses, top thumb knuckle to thumb tip for the inch, etc). A classic example of one of these units is the foot. This applies, not only to the imperial foot, but to the other foot units historically used in different cities and countries.

In order for any measurement unit to be useful, it needs to be a standard size. So whose foot size would be the basis for the unit of the same name? That is anyone’s guess. Go to any shoe shop and you will find many different shoe sizes. Even they must be measured somehow to fit customers’ feet.

I recently came across a website for Shoe Size Converter Charts (website: It contains conversion tables for American, European and British shoe sizes with equivalents shown in inches and centimetres for men, women, youth and infants. For the same shoe numbers, men’s sizes are slightly larger than women’s.

On the Shoe Sizing Charts website, let’s look at the UK sizes for men. It lists a total of 17 sizes, increasing by 0.5 from size 5.5 to size 11.5 and by 1 from size 11.5 to size 15.5. At the lower end of the scale for UK men’s shoe sizes, size 5.5 = 23.5 cm, size 6 = 24.1 cm and size 6.5 = 24.4 cm. At the top end of the scale for UK men’s shoe sizes, size 12.5 = 29.4 cm, size 13.5 = 30.2 cm, size 14.5 = 31 cm and size 15.5 = 31.8 cm. National shoe shops (e.g. Clarks, Asos) give slightly different conversions for shoe sizes.

The closest size to the imperial foot in the Shoe Sizing Charts is the UK men’s size 13.5. So you will need at least a men’s size 13 to get an equivalent shoe size to the imperial foot (30.48 cm), an unusually large foot size. For women’s shoe sizes, the imperial foot is off the scale on the same website. The top UK women’s shoe size there is a size 10, equivalent to 27.6 cm.

The size of the imperial foot is not a typical foot size for most people. For the unit called the foot, you will find a wide range of measures for the foot on Wikipedia, most of which are now obsolete.


14 thoughts on “An unnatural foot”

  1. A natural unit that survives is the mile. It is derived from a Roman unit, the passus, which was two steps of a Roman legionary or about 1.5 m. A thousand passus was called a mille passus, which has come down to us as the mile. Strange that a measurement we see as (non-decimal) imperial is actually a thousand of something. Well at least it was Roman imperial too – they occupied most of Britain for almost 400 years and this is one of their legacies. Incidentally there were 5 feet in a passus so 5000 Roman feet in a Roman mile (or mille passus) compared with 5280 imperial feet in an imperial mile – trust us to make things more complicated than they need be.


  2. Just recently Fernando provided this link on the Egyptians and how they used a water drop that was exactly 1 cm in width as a base of their measuring system. The foot and other body parts were considered unworkable since they varied from person to person and this was mentioned in the video.

    The discussion of the Egyptians weights and Measures starts just after 45 min. When I clicked on the link provided it took me past 1 h into the video, so I had to slide the time bar back to about 45 min. It is highly advisable to watch this section of the video where this is discussed.

    Also, since the language is French I tried to activate the closed captioning and it turned out it defaulted to Macedonian. But, I was able to change it to auto-translate and select English.


  3. @Daniel Jackson

    So, you didn’t learn French at school?
    Quelle horreur! 😉

    (I lived in France, so please excuse my bias. Vive la France! Vive le Royaume Uni!)


  4. The sacred barley corn lives. Note that all the inch fractions have been rounded to the usual binary fractions, but three sizes is an inch in those charts.


  5. Ezra,

    Ich studierte deutsch zur Schule. Französisch ist nur germanisiertes Latein.


  6. I don’t think the bare foot was intended to be the measuring unit. It was the foot with a shoe on. Back in the day when 16 men were forced to form a line exiting the church to be measured for the standard, they left their shoes on.

    This may explain why a “foot” is closer to 30 cm and not 25, which is the approximate length of the average bare foot.


  7. Daniel, yes, that shoe is the explanation we got at school. The difference, being very British about it, it was the King’s shoe. Either way that ‘foot’ should in fact be a ‘shoe’. The ‘foot’ may have had other origins.


  8. Daniel Jackson, It is good to see them so rattled, they just can’t handle the fact that the British public are perfectly capable of working and understanding metric measures. I haven’t come across anyone complaining about it in my every day life. The majority of people are actually more concerned with staying safe, keeping infection down and getting the country back on course, all the BWMA can complain about is metric measurements, says it all really.


  9. Gavin,

    It’s unfortunate that the Fake News outlets always quote the BWMA and never ask the UKMA for their opinion. Real News would quote both sides and not bias the reader. It was good to see some of the comments to the Telegraph article making the same conclusion as yours.


  10. Daniel, the reality of these sorts of “fake news” articles is that organisation XYZ have a press release which only gives their side of the story. Daily newspapers do not have time to interview the other side, especially if reporters need to get their copy to the editor by a specific deadline, If it appears to be a “good” story and competitior newspapers will be running it, then they are even more desparate to get their copy in place without any spelling or grammatical errors rather than to get all the facts. As the French say “c’est la vie”.


  11. @ Derek:

    I disagree about the mile being a ‘natural’ unit. I doubt very much whether Roman legionaries 2000 years ago were all the same height and weight and so all had the same ‘natural’ stride, two steps of which were the passus. I’m sure the passus was as much a standard stride invented by their military rulers as the lengths of strides for various purposes in the armed forces are today.


  12. Just came across a fine video about how unnatural all Imperial units are and the advantages of using the metric system:

    This is part of the Real Engineering video series, many of which I have found both useful and enlightening.


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