Inches to fraction calculator

A drawing, a spec sheet or a digital caliper gives a decimal. A tape measure gives fractions. This inches to fraction calculator takes the decimal and finds the nearest mark, and it shows how far off that mark is, so you can decide whether the difference matters for the job. The chart lists every sixty-fourth from 1/64 to 1 in with its decimal and its millimetres.

Reading fractions on a tape measure

Between two inch marks, the longest line is the half inch. The next longest are the quarters, 1/4 and 3/4, then the eighths, and the shortest lines are the sixteenths. To read a measurement, take the last whole inch and count the lines past it in sixteenths: the seventh line past the 3 in mark is 3-7/16 in. Then reduce: 8/16 is 1/2 and 12/16 is 3/4. Some tapes mark thirty-seconds along the first foot.

Decimal inches to the nearest fraction

Multiply the decimal by the finest mark you work to, round to a whole number, and put it over that mark. For sixteenths, 0.44 × 16 = 7.04, which rounds to 7, so the nearest mark is 7/16". Then reduce: 8/16 is 1/2", and 12/16 is 3/4". The calculator does all of this and also gives the mark below and the mark above.

Millimetres to inches as a fraction

Divide the millimetres by 25.4 for decimal inches, then find the nearest mark. 10 mm is 0.3937 in, which is 3/8" to the nearest sixteenth and 25/64" to the nearest sixty-fourth. Choose MM above and type the plain number, or type 10mm with any setting. Drill bits and hardware sold in metric often need this conversion.

Decimal feet to feet and inches

A decimal foot is not an inch. 5.7 ft is 5 ft 8-3/8 in, not 5 ft 7 in, because 0.7 ft is 8.4 in. Surveys and civil drawings use decimal feet, and carpenters use fractions. Choose FEET above, type the decimal, and the answer comes back in feet and inches to the mark you picked.

Which mark to round to

Use the finest mark you can actually cut to. Framing works to a sixteenth. Finish carpentry and cabinetry often work to a thirty-second. The error row tells you what rounding costs. At 1/16 no answer is more than 1/32 in, or 0.79 mm, from the true value. At 1/64 no answer is more than 1/128 in, or 0.2 mm, away.

The mark below and the mark above

The nearest mark is not always the one to cut to. A part that has to fit inside an opening should be cut to the mark below, and a part that has to cover a gap should be cut to the mark above. Both are shown so the choice is yours, not the rounding rule's.