Fractional Inch to Decimal Converter

Every fraction equals its numerator divided by its denominator. 3/8 means "three eighths": three of the eight equal slices that make up one inch. Divide 3 by 8 and you get the decimal value directly: 3 ÷ 8 = 0.375 inches, which is 0.375 × 25.4 = 9.525 mm.

The same division works regardless of the denominator. 11/32 = 11 ÷ 32 = 0.34375 inches (8.73125 mm). 15/64 = 15 ÷ 64 = 0.234375 inches (5.953125 mm). 17/32 = 17 ÷ 32 = 0.53125 inches (13.49375 mm). No simplification step is needed for this direction, since you are not reducing a fraction, you are evaluating one.

Converting a fraction to decimal is always exact, unlike converting a decimal to a fraction. Dividing 7 by 64 gives exactly 0.109375, with no approximation involved, because the division terminates. This is different from the decimal-to-fraction direction, where a chosen precision like 1/16" or 1/64" forces the calculator to round to the nearest available fraction.

The only case where this direction is not perfectly exact is a fraction with a denominator that is not a power of 10 or 2, like 1/3 or 1/7, which produce a repeating decimal (0.333…). Every inch fraction used in construction, woodworking, and machining has a power-of-two denominator, so this repeating-decimal case never comes up in practice.

Once you have the decimal-inch value, centimeters and feet fall out of the same two multiplications used throughout this site. Multiply decimal inches by 2.54 for centimeters, or divide by 12 for feet. 9/16" = 0.5625 inches = 1.42875 cm = 0.046875 ft.

These conversions matter most when a plan mixes unit systems, which happens often with imported hardware or fixtures specified in millimeters next to a drawing specified in inch fractions. Converting both sides to decimal inches, or both to millimeters, before comparing removes any guesswork.

Add 5/8" and 3/16" without a common denominator by converting each to decimal first. 5/8 = 0.625. 3/16 = 0.1875. Adding them gives 0.625 + 0.1875 = 0.8125 inches.

Check the result by converting 0.8125 back to a fraction: 0.8125 × 16 = 13 exactly, so the sum is 13/16" with no rounding needed. You can confirm this the traditional way too: rewrite 5/8 as 10/16, add it to 3/16, and you get 13/16, the same answer both routes give. In millimeters, 0.8125 × 25.4 = 20.6375 mm.

CAD software, CNC toolpaths, and spreadsheets all expect decimal input, not fractions, because decimals are far easier to add, scale, and compare programmatically. A dimension entered as 0.4375" moves cleanly through a formula, while a dimension entered as "7/16 inch" would first need to be parsed and evaluated.

Calipers and micrometers also read in decimal inches, so converting a drawing's fractional callouts to decimal lets you compare a measured part directly against the spec without doing mental division on the shop floor. Use the mixed number calculator if the drawing includes a whole-number part, like 2 5/8", or the main decimal to inches tool to go the other direction.

If you already have a decimal and need the closest inch fraction, use the decimal to fractional inch converter instead, which lets you pick a precision (1/8, 1/16, 1/32, or 1/64) and rounds accordingly. Both calculators use the same 25.4 mm-per-inch conversion factor, so results always agree in the middle.

For a general decimal-to-fraction conversion that is not limited to inch-style power-of-two denominators, the decimal to fraction calculator reduces any decimal to its simplest fraction using the Greatest Common Divisor.