Measuring and converting
Inch fraction chart: fractions to decimals and millimeters
A tape measure reads in fractions, a plan may give decimal feet or inches, and a European tool wants millimeters. This chart has every sixteenth of an inch in all three, and the rules to go back the other way.
Fractions of an inch to decimals and millimeters
An inch is exactly 25.4 mm, so these millimeter values are exact, not rounded.
| Fraction | Decimal inch | Millimeters |
|---|---|---|
| 1/16 in | 0.0625 | 1.5875 |
| 1/8 in | 0.125 | 3.175 |
| 3/16 in | 0.1875 | 4.7625 |
| 1/4 in | 0.25 | 6.35 |
| 5/16 in | 0.3125 | 7.9375 |
| 3/8 in | 0.375 | 9.525 |
| 7/16 in | 0.4375 | 11.1125 |
| 1/2 in | 0.5 | 12.7 |
| 9/16 in | 0.5625 | 14.2875 |
| 5/8 in | 0.625 | 15.875 |
| 11/16 in | 0.6875 | 17.4625 |
| 3/4 in | 0.75 | 19.05 |
| 13/16 in | 0.8125 | 20.6375 |
| 7/8 in | 0.875 | 22.225 |
| 15/16 in | 0.9375 | 23.8125 |
| 1 in | 1 | 25.4 |
A thirty-second is 0.03125 in (0.79375 mm) and a sixty-fourth is 0.015625 in (0.396875 mm).
How do you read a tape measure?
The longest lines are the inches. Between them, the next longest line is the half, then the quarters, the eighths and, shortest, the sixteenths. Count the sixteenth lines past the last inch and reduce the fraction: 6 lines past 3 in is 3 6/16, which is 3 3/8 in.
What are the red and black marks on a tape?
Many tapes mark every 16 in, often in red, for studs and joists at 16 in on center, and put a small black diamond every 19.2 in, which divides 8 ft into five equal spaces for trusses. Not every brand does both.
Why does the hook move?
The hook at the end slides by its own thickness, so the reading is true both when you hook it over an edge and when you push it against a wall. Do not bend it back tight.
How do you convert a decimal to the nearest sixteenth?
Multiply the decimal part by 16 and round to a whole number: that is the number of sixteenths. Then reduce the fraction.
Example. 0.43 in × 16 = 6.88, which rounds to 7, so 0.43 in is about 7/16 in (0.4375 in).
How do you convert millimeters to inches and fractions?
Divide by 25.4 for inches, then turn the decimal part into sixteenths as above.
Example. 100 mm ÷ 25.4 = 3.937 in. 0.937 × 16 = 14.99, so 15 sixteenths: 3 15/16 in, which is off by less than a thousandth of an inch. Going the other way, 3 5/8 in × 25.4 = 92.075 mm.
Fractions in Clad
Clad holds every length as a whole number of 1/64 inch and rounds only the answer you see, to 1/16 in unless you choose otherwise, and it says which rounding it used. The calculator shows decimal inches under every result and can show millimeters side by side.