To measure without a ruler, use an object with a standardized size: a US dollar bill is 6.14 inches long, a bank card is 3.37 inches wide, a quarter is 0.955 inches across, and US letter paper is 8.5 by 11 inches.
Money, bank cards and printer paper are all made to exact sizes. That makes them rulers.
You are in a shop looking at a shelf, or at home wondering whether a frame will fit, and there is no tape measure. You probably have a good one anyway. Coins, banknotes, cards and paper are manufactured to tight specifications, so they are far more reliable than a guess.
| Object | Size in inches | Size in mm |
|---|---|---|
| US penny, diameter | 0.75 | 19.05 |
| US nickel, diameter | 0.835 | 21.21 |
| US quarter, diameter | 0.955 | 24.26 |
| Bank or credit card, long edge | 3.37 | 85.6 |
| Bank or credit card, short edge | 2.125 | 54 |
| US dollar bill, long edge | 6.14 | 156 |
| US dollar bill, short edge | 2.61 | 66.3 |
| US letter paper | 8.5 by 11 | 216 by 279 |
| A4 paper | 8.27 by 11.69 | 210 by 297 |
That is close to every length you need in daily life. A row of four quarters is just over 3.8 inches. Two dollar bills end to end make 12.28 inches, so about a foot.
Short references get less accurate as you repeat them, because each step adds a small error. These tricks help:
If you have an iPhone, Apple's built-in Measure app estimates lengths through the camera. It is handy for rough sizes, though a dollar bill will often beat it on small objects.
US coins are minted to exact weights, so they double as a small set of gram weights:
| Coin | Weight |
|---|---|
| Penny (1983 or later) | 2.5 g |
| Nickel | 5 g |
| Dime | 2.268 g |
| Quarter | 5.67 g |
A nickel is the easy one to remember. Twenty nickels weigh 100 grams, which is about 3.5 ounces.
To use them, build a simple balance. Rest a ruler or a stiff strip of card across a pencil, and center it until it sits level. Put the mystery item at one end and add coins at the same distance on the other end until it balances. Add up the coins. Friction will throw off the result a little, so treat it as an estimate, not a lab reading. It will still settle whether your letter needs a second stamp.
Finding a middle is easier than measuring a length, because you can skip the numbers:
That last point catches people out. The middle of an odd shape is rarely where it looks. We wrote a whole piece on where the middle of an object actually is, and the same trouble appears when you try to judge weight by hand.
Sometimes there is nothing to measure with at all. Your eye does better if you give it a comparison. Picture a known object next to the unknown one, then count how many would fit. Check by flipping the comparison: if the shelf looks like three dollar bills wide, ask whether it could really be four.
If you want to practice with a real score attached, Halfsies is a free daily game built on this skill. You get three hand-drawn objects a day, you cut each one in half by eye, and a scale weighs both sides. No ruler allowed.
A US dollar bill is about 6.14 inches long and 2.61 inches wide, or 156 by 66.3 millimeters. All current US paper money is the same size.
A US quarter is the closest common object at 0.955 inches across. For a truer inch, mark a quarter's width and add a tiny bit more, about the thickness of a pencil line or two.
Lay two US dollar bills end to end for 12.28 inches, or use the long edge of letter paper, which is 11 inches, and add about one more inch.
Nearly all bank and credit cards follow the ID-1 standard in ISO/IEC 7810, which sets them at 85.6 by about 54 millimeters.
A US nickel, which is minted to weigh 5 grams. Two pennies made since 1983 also add up to about 5 grams.