Measure it with your hand

Two units, people say, one long and one short. Many people use the hand span — thumb-tip to little-finger-tip with the hand spread — as the long one, and give it as roughly eight to nine inches for an adult; one person prefers the wrist-to-middle-fingertip length instead, and some people argue the span is more useful for its size. Many people use the thumb as the short one: the width of the thumb, or the length of its first joint, is close to an inch on the people who measured, and one person puts the thumb’s first knuckle, measured across, at about an inch. Some people add elbow to fingertip as roughly a foot — the old cubit, some say — and others add the palm, the shoe and the stride as the other classical units. One person says an adult hand is about four inches across, and people argue whether that holds: one person says theirs measures four inches too, and people’s conclusion is that it is a common average and not a promise. Another person points out that a hand is exactly what horse people mean by a hand — four inches — which matches the average, one person says.

Rough enough that people set out the limits as carefully as the trick. Some people warn body parts vary and nothing about them is standardised; people add, one person each, that hands change with weight, that a finger with an old injury will not measure true, that your dominant hand and your other hand are not quite the same size, and some people warn that a measurement memorised young leads to persistent errors, because you grew and the number did not. One person says that having measured their finger with itself they can report it is about one finger long: you cannot get a fraction out of a body part without a ruler first, one person objects, so calibrate against a real one and then trust the copy. Some people recommend memorising the hand you do not write with, so the other is free to hold a pen or a tool while you measure. How to calibrate properly, and how far out these estimates typically are against a tape, are asked and not answered — a gap. People’s own answer to precision is a coin or a ruler, not a finger, and this page agrees.

Some people reach for money before fingers, and others say the same: a banknote or a coin has a fixed size and does not grow. The one figure people argue over is the US dollar bill — some call it six inches long — and one person corrects it: a US note is 6.14 inches long and 2.61 inches wide, the same for every denomination, which this page checked against the Bureau of Engraving and Printing’s own document and carries as its own line. Some people fold the note in half for three inches; one person says a US quarter is about an inch across; one person says an Australian five-dollar note is thirteen centimetres; one uses a sheet of US letter paper, eight and a half by eleven. Some people warn older notes can differ in size through wear or changes in manufacture, and that sizes differ between countries and eras. Some people say a phone or even a banana will do as a proxy if you know its length, and people argue whether a thing in your pocket beats a thing on your arm, some people on each side — the decider is whether you have the object to hand or only your hand.

People scale up the same way. Some people say learn your stride and count paces for a room or a garden, and people argue whether stride is any use, one person on each side — one person warns it varies a good deal from day to day, and one person prefers the forearm because a forearm that changed length would hurt. One person measures a doorway or a sofa by stretching an arm sideways and taking the distance from the far shoulder to the fingertips as roughly a metre; one uses the height of their own hip bone from the floor as a vertical mark; one extrapolates from a known width to the building across the street. All of it inherits the same caveat as the hand, and people do not pretend otherwise: it is a rough visual scale, some people object, not a ruler without markings.

Some people describe it: hold your arm out straight, stack your fingers sideways between the bottom of the sun and the horizon, and count roughly fifteen minutes of daylight left for each finger. Read the safety line before you try it — do not look at the sun, cover it with your hand. Then the mistakes people caught and the limits, of which people have many. One person points out to measure along the sun’s actual path down to the horizon, not straight down, and that at very high latitudes it still fails; some people say daylight-saving changes what the clock says and nothing about how long the light lasts. Some people warn the method fails in high latitudes, where the sun sets at a shallow angle or, in summer, does not set at all; one person warns you need a visible horizon, which mountains take away; one person says it varies with the season. People argue whether the method works everywhere or only where you have calibrated it, and the decider people give is where you are on the globe and how long your own arm is; people also argue whether arm length and finger width cancel out — they roughly do, some people say, because long arms come with wide fingers — or need personal calibration, and one person settles it for hikers: it is a quick, low-tech estimate for planning camp or the hours of walking left, not a precise time. One person says altitude changes the answer by less than the trick’s own error.

Mostly, and not entirely. Many people suggest a ruler tattooed along the forearm as the permanent fix; some people describe a fashion designer who did have a scale tattooed on a finger so she never has to hunt for a tool. People argue body parts against coins and rulers — some people say a finger is convenient and good enough for a rough idea, and some people say it is too variable and a coin is better — and people’s decider is what the number is for: a rough visual scale, or real precision, which wants a coin or a ruler. Some people say the newer phone cameras measure for you and make all of this unnecessary, and the people who still use a hand say they do it because the hand is always there. Some people have used their hands this way for decades or since childhood, and one person says the trick came down through family.