Are imperial feet “natural” units?

With the slow transition to metric in the UK, a lot of myths have emerged regarding metric and imperial. With a New Year it is an appropriate time to examine some of these myths starting with the claim that imperial feet are ‘natural’ units.

Despite the end of the British Empire and the demise of the pith helmet, quite a few British people are nostalgic about imperial units. However, many people are not really proficient in using them and often are ignorant about their history and usage. For example many people do not know how many yards are in a mile. When the Times carried out a straw poll in early 2006 answers given for yards in a mile ranged from 52 to 10 000. The vast majority of people – even elderly – cannot explain how an acre is defined.

It has been often claimed in the British news media and by imperial supporters that imperial units are ‘natural’. Yet no evidence is offered to support this. What part of the body weighs a pound? What volume naturally corresponds to a pint? Maybe the obvious example is to say that the imperial foot is a “natural unit”.

However, a little thought shows that this is an empty claim. A unit needs to have a standard size otherwise there would be complete chaos. Human feet are not a standard size and so there is no natural size for the unit. The fact that human feet vary led to many different standard feet in Europe in the past; a key reason why an international system (metric) was needed.

In fact very few people have feet that are as large as the imperial foot; you would need a British “shoe size 12 ½” foot! The vast majority of people have smaller feet (the photo above shows 3 people measuring their feet against a scale in inches). The average human foot is 24 cm versus 30.48 cm for the imperial foot. If an imperial foot is “natural” then by implication most people have unnaturally small feet! If in doubt try measuring your own feet and those of your friends and family.

A much stronger argument is that decimal numbers are “natural” since all able bodied people have ten digits. It is nonsensical to justify keeping imperial on the basis that the units are “natural”; parts of the body are non-standard and so quite unsuitable as the basis of modern measures. Far better to use the accurately-determined and easy-to-use metric units.

[See also related article at http://www.metricviews.org.uk/2007/10/28/imperial-units-natural/ – Ed]

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