Measure it with your hand

Two units, the accounts say, one long and one short. Six separate conversations 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 account prefers the wrist-to-middle-fingertip length instead, and one exchange, one account to two, argues which is more useful, with the span winning on size. Six separate conversations 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 accounts who measured, and one account puts the thumb’s first knuckle, measured across, at about an inch. Two conversations add elbow to fingertip as roughly a foot — the old cubit, two conversations say — and two more add the palm, the shoe and the stride as the other classical units. One account says an adult hand is about four inches across, and one exchange, two accounts to one, argues whether that holds: one account says theirs measures four inches too, and the accounts’ conclusion is that it is a common average and not a promise. Another account points out that a hand is exactly what horse people mean by a hand — four inches — which matches the average, one account says.

Rough enough that the accounts set out the limits as carefully as the trick. One caution, two accounts strong, says body parts vary and nothing about them is standardised; single cautions add 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 — two accounts — that a measurement memorised young leads to persistent errors, because you grew and the number did not. One account 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 objection says, so calibrate against a real one and then trust the copy. Two accounts 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 in these conversations and not answered — a gap. The accounts’ own answer to precision is a coin or a ruler, not a finger, and this page agrees.

Three separate conversations reach for money before fingers, and two more say the same: a banknote or a coin has a fixed size and does not grow. The one figure the accounts argue over is the US dollar bill — several call it six inches long — and one correction fixes 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. Two conversations fold the note in half for three inches; one account says a US quarter is about an inch across; one account says an Australian five-dollar note is thirteen centimetres; one uses a sheet of US letter paper, eight and a half by eleven. Two cautions, two accounts each, say older notes can differ in size through wear or changes in manufacture, and that sizes differ between countries and eras. Two conversations say a phone or even a banana will do as a proxy if you know its length, and one exchange, two accounts to two, argues whether a thing in your pocket beats a thing on your arm — the decider is whether you have the object to hand or only your hand.

The accounts scale up the same way. Two conversations say learn your stride and count paces for a room or a garden, and one exchange, one account each way, argues whether stride is any use — one caution says it varies a good deal from day to day, and the account on the other side prefers the forearm because a forearm that changed length would hurt. One account 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 the accounts do not pretend otherwise: it is a rough visual scale, one objection says, not a ruler without markings.

Three separate conversations 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 corrections and the limits, of which the accounts have many. One correction says to measure along the sun’s actual path down to the horizon, not straight down, and that at very high latitudes it still fails; two accounts in one correction say daylight-saving changes what the clock says and nothing about how long the light lasts. One contraindication and three cautions — one rated high, three accounts — say the method fails in high latitudes, where the sun sets at a shallow angle or, in summer, does not set at all; one caution says you need a visible horizon, which mountains take away; one says it varies with the season. One exchange, one account to four across two conversations, argues whether the method works everywhere or only where you have calibrated it, and the decider the accounts give is where you are on the globe and how long your own arm is; two more single exchanges argue whether arm length and finger width cancel out — they roughly do, one side says, because long arms come with wide fingers — or need personal calibration, and one account 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 account says altitude changes the answer by less than the trick’s own error.

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