One of the claims sometimes made by defenders of imperial weights and measures is that they are “natural”. The metric system (they may say) is all very well for science and technical matters, but for everyday life imperial units like the foot conform to the human scale and are more “natural”, unlike the arbitrary metric unit, the metre. We examine this argument.
In the first place, if a unit of measurement is to be useful it must necessarily be arbitrary – that is, it must have the same assigned value anywhere and everywhere. People’s feet are not all the same length, and in any case not many people even know how long their foot is! That is why the 1824 Weights and Measures Act standardised imperial units (like the foot and the mile) so that they would be the same in every region of the country, thus reducing the opportunity for traders to cheat their customers.
Even if the imperial foot was based approximately on the length of a real person’s foot, that person must have had very big feet. (A typical adult man’s foot, taking a size 9 shoe, would be about 260 mm long, whereas an imperial foot is 305 mm.)
Similarly, there is nothing particularly “natural” about the pint or the gallon. If there were, it would be difficult to explain why what is “natural” for Americans is smaller than what is “natural” for the British and Irish – or even Canadians. (An US gallon is 3.785 litres, whereas an imperial gallon is 20% larger at 4.546 litres).
Of course the truth is that when people say that measurement units are “natural”, what they mean is that they are what they are used to. Just in the same way as it is “natural” to speak English – except in most of the world.
To people brought up in exclusively metric countries, litres, metres and kilograms also seem “natural”. Some continental European correspondents have provided the following examples of how working in metric is “natural” for them, enabling them to devise various rules of thumb.
CK (German) writes:
“To me, metric is much more “natural”, i.e. linked to the body, the planet or nature in general. Just have a look at the statistics below. However, all figures are approximations, as nature does not produce things in uniform sizes:
Normal walking speed for a human on flat ground: 6 km/h [actually, this is fairly brisk – Ed]
This equates to 1 km every 10 min or 100 m every 1 min. Metric allows me to estimate distance by walking and checking the time. Or conversely, I know how long it takes me to walk between two points on a map.
For rough terrain, [or leisurely walking] halve the figures above (1 km every 20 min).
Average speed of a car on a fast road (motorway): 100 km/h
This makes a 550 km trip 5.5 h long.
Average speed of a car on a normal road: 60 km/h
This makes a 30 km km trip 0.5 h long.
Normal pace (double-step) of average humans: 1 m
Average height of men: 1.75 m
Average height of women: 1.65 m
Circumference of the earth: 40 000 km
Thickness of a fingernail: 1 mm
Width of a finger: 1 cm
Width of a hand: 10 cm
Average annual precipitation (rain, snow, hail, etc.) in most countries with moderate climate (i.e. most of Europe, North America): 1 m = 1 000 mm
1 cm of snow = 1 mm of water = 1 L/m² = 1 kg (Can’t be easier.)
1 liter of water and most common liquids: 1 kg
1 cubic meter of water and most common liquids: 1 t
1 ml of of water and most common liquids: 1 g = 1 cm³
Volume of water humans should drink per day: 2 L
Normal weight range for newborns: 2.5 kg to 4.5 kg
Average weight for newborns: 3.5 kg
Weight that normal people can lift without severe difficulties: 50 kg
Average weight for women: 65 kg
Average weight for men: 75 kg
Normal body weight for humans: Height in cm minus 100 = weight in kg
Weight of an average, small car 1000 kg = 1 t
Water freezes/ice melts: 0 °C
Water boils: 100 °C
Comfortable temperature, room temperature: 20 °C
Human body temperature: 37 °C
Fever: Temperature above 38 °C
Skin contact starts to get painful at 50 °C
Current potentially deadly for humans: 50 mA
Safe limit for radioactivity in food: less than 500 Bq/kg
Standard light bulb: 500 lm, 100 W
Illumination required for an office: 500 lx
Illumination outside on a cloudy day: 10 000 lx
Illumination outside on a sunny day: 100 000 lx
Water pressure for household pipes 200 kPa
Pressure rises 10 kPa for each meter under water.
One hectare: 100 m x 100 m
Distance to the moon: 300 000 km
Distance to the sun: 150 million km
You will notice that all the figure are nice, round and easy to remember. The list is endless. You could continue with temperature drop, or pressure per 100 m elevation, mixture of flour and water for bread’ etc.
In my experience, people who grew in metric countries are much better at estimating und understanding weights and measures than people brought up in dual-measure countries (i.e. Britain, Canada).
Try to ask a person in Britain: What is an acre? How much does it cost to fill a swimming pool? How much does this letter weigh? You will hardly get reasonable answers. I have experienced so many intelligent, well-educated, numerate people here who frequently or at least occasionally completely screw up a measurements and display a sometimes complete lack of comprehension. It is easy for me to have a “relationship” to a kilogram, I know how much it is. For a person, who is confronted with ounces, pounds, stones, tons, grams and kilograms, it is not so easy. They confuse things, they don’t have a firm foundation. I have seen a pharmacist completely helpless in trying to remember an average baby’s weight, a nurse unable to calculate 10 % weight loss – and there are many more examples. I don’t have the same experiences in metric countries.
To me, metric is more natural. The oldest measurement unit we know about is the ell. Surprisingly, the oldest known ell is pretty much exactly 50 cm. If this ell was a natural unit, then so is the meter.”
And here is a similar comment from WB, who is Danish:
“As you have already guessed, I can assure you that my countrymen have no difficulty in judging distances, sizes, weights, speed etc. using the metric system. I can further assure you that we consider metric units completely “natural” (if that’s the term we are debating here). As you say, what you are familiar with (like your mother tongue) feels “natural”.
Apart from that, it is nonsense to suggest that imperial units are more “natural” than metric units. The size of a foot obviously varies from person to person (yesterday, I stood next to a young man whose foot was about 50% longer than mine!). Therefore the unit “foot” is completely arbitrary and the same goes for lots of other units (like inch or fathom, say).
As for metric units – it would be only too easy to give examples of their “naturalness”, if that’s what you want. E.g. a metre is the distance from the ground to my belly buttton (yes, absolutely spot on). Two metres is the height I can comfortably reach when I raise my arm above my head. And a cm is the width of my little finger. As for weight (like a kilo) and volume (like a litre) you acquire a feel for these quite “naturally” when you grow up with them (although in actual fact it takes no more than a few minutes if you put your mind to it). The fact that a ton(ne) is 1000 kilos is also quite easy to grasp for a normal person, and the same goes for a cubic metre (1000 litres). What about 100 metres? Well, that is the shortest sprint distance run by atheletes and nobody here or abroad seems to have the slightest difficulty with that. “Natural”, wouldn’t you say? And what’s a comfortable temperature, both indoors and outdoors? That’s a nice round 20 degrees. And 100 degrees is the temperature at which water starts to boil, of course. I find that very natural.
Many units used to be more or less loosely connected with agriculture (not only here but everywhere), because most people worked in agriculture and lived in the country. Hence an acre = what a span of oxen can plough in half a day (I think is the definition). Not very accurate, of course, since this will vary with the terrain, the soil, the weather, the strength of the animals, the equipment and the skill of the ploughman. The relevance to the way of life today is non-existent and into the bargain, the size and subdivision of this funny unit are so awkward that it is almost impossible to use for calculations if you are not a maths professor. All in all a totally useless unit that could hardly be described as “natural”, certainly not today. No wonder that the vast majority of people in this country have no idea what an acre is. Give me a square metre or a hectare any day – they never vary, are dead easy to visualise and dead easy to use for calculations. These advantages are so enormous that I would say that these units feel very “natural”.
I shall never forget that when I was at secondary school and later at business school, as part of our training we had to do “English” invoices, i.e. not only in awkward money like £sd but also for quantities like tons, hundredweights, quarts, pounds and ounces (consignments of coal for instance). None of this seemed in the slightest “natural” to any of us. To say that it was a nightmare and that we hated it, is an understatement. Imagine our relief when we heard that the UK was going both metric and decimal and that we could forget about imperial units and “English” invoices! At least we in Denmark were then spared further punishment – unlike people in this country who are still suffering from having to live with imperial units 40 years later! If that’s “natural”, give me “unnatural”, please!”