Inches to Fraction Converter
Type a decimal inch measurement and get the nearest tape-measure fraction — reduced to lowest terms, with the exact rounding error shown. 0.625 in converts exactly to 5/8 in.
Example: with Decimal inches 0.625 · Precision Nearest 1/16 inch (tape measure) → Nearest fraction: 5/8 in.
Computed by the calculator below using its default values. Change any input to see your own numbers.
📏 Measure finer with a 1/64-marked tape
Check it outDecimal inches to fractions, the tape-measure way
To convert decimal inches to a fraction, multiply the decimal part by your precision denominator, round to the nearest whole number, and reduce. For 0.39 inches at sixteenths: 0.39 × 16 = 6.24, which rounds to 6, so 6/16 reduces to 3/8 in with a rounding error of −0.015 in. Some decimals convert exactly — 0.625 is precisely 5/8, 0.375 is 3/8, and 0.75 is 3/4 — because they sit right on eighth-inch marks.
Precision changes the answer. 0.4 inches is 3/8 at the nearest 1/16 but 13/32 at the nearest 1/32 (error only +0.006). Likewise 0.2 in ≈ 3/16 and 0.8 in ≈ 13/16 on a standard tape, each off by 0.0125 in. Most US tape measures mark sixteenths, so 1/16 is the practical default; switch to 1/32 or 1/64 for machining or fine woodworking.
How it’s calculated
The tool multiplies the decimal part of your measurement by the chosen denominator (8, 16, 32, or 64), rounds to the nearest whole numerator, and reduces the fraction by its greatest common divisor (10/16 → 5/8). Rounding error = fraction value − input value; the worst case is half of one increment, e.g. 1/32 in (0.03125 in) when rounding to sixteenths.
Results update as you type and are estimates, not professional advice — verify important decisions with a qualified professional.
Common mistakes
- Reading the reduced fraction against unreduced tape marks — 5/8 sits on the 10/16 line.
- Using sixteenths for precision work: rounding to 1/16 can be off by up to 0.031 in; use 1/64 instead.
- Dropping the whole inches — 2.7 in converts to 2 11/16 in, not 11/16 in.
Frequently asked questions
What is .39 inches as a fraction?
To the nearest 1/16 it's 3/8 in (0.39 × 16 = 6.24, rounds to 6/16). At 1/64 precision it's 25/64 in (0.390625), only 0.0006 in off.
What is .4 inches as a fraction?
Exactly 2/5, but tape measures don't mark fifths. The nearest 1/16 is 3/8 in (0.375) and the nearest 1/32 is 13/32 in (0.40625).
What is .2 inches as a fraction?
Exactly 1/5; on a sixteenths tape the nearest mark is 3/16 in (0.1875), an error of −0.0125 in. At 1/64 precision it's 13/64 in (0.203125).
What is .8 inches as a fraction?
Exactly 4/5; the nearest 1/16 is 13/16 in (0.8125). If you need tighter accuracy, 51/64 in (0.796875) is within 0.004 in.
Why do the fractions use 8, 16, 32, and 64?
Inch rules are divided by halving: halves, quarters, eighths, sixteenths, and so on. Most US tape measures mark 1/16 in, while machinist rules go to 1/64 in.