Inches to Decimal Calculator

Divide the numerator by the denominator, then add any whole number in front. Five-sixteenths (5/16) becomes 5 ÷ 16 = 0.3125. Eleven thirty-seconds (11/32) becomes 11 ÷ 32 = 0.34375. For a mixed number, convert the fraction first and add it to the whole number: 2 5/8 becomes 2 + 0.625 = 2.625.

The calculator above does this division automatically and also returns the millimeter, centimeter, and feet equivalent for the same value, so a separate lookup for each unit is not needed.

A blueprint or tape measure callout is usually a whole number plus a fraction, so here is how five common readings convert. 4 5/8 inches: 5 ÷ 8 = 0.625, so 4 5/8 = 4.625 inches (117.475 mm). 7 3/16 inches: 3 ÷ 16 = 0.1875, so 7 3/16 = 7.1875 inches (182.5625 mm). 11/64 inch on its own: 11 ÷ 64 = 0.171875 inches (4.365625 mm), a size that shows up often on aircraft-grade drill bit charts. 27/64 inch: 27 ÷ 64 = 0.421875 inches (10.715625 mm). 12 1/2 inches: 1 ÷ 2 = 0.5, so 12 1/2 = 12.5 inches (317.5 mm). Each result is exact, since 8, 16, 64, and 2 are all powers of 2.

A rounding error of even 0.001 inch can be the difference between a part that fits and one that does not, especially in precision machining where tolerances are held to a few ten-thousandths of an inch. Converting 17/32 to 0.53 instead of the exact 0.53125 introduces an error of 0.00125 inch, small on paper but large enough to fail an inspection on a tight fit. This calculator carries every digit through the division and only rounds when a fractional precision is explicitly chosen, so the decimal display is always exact rather than an approximation.

The table below lists every standard fraction from 1/64 to 1 inch with its decimal and millimeter equivalent, so a value can be looked up instead of doing the division by hand each time.

The same chart works whether the starting point is a fraction or a decimal. Look up a fraction like 23/32 in the left column to get 0.71875 inches on the right, or scan the decimal column for the closest match to a reading from a caliper or CAD file, then read off the standard fraction next to it. If a decimal falls between two rows, the calculator above rounds it to the nearest fraction at a chosen precision instead of leaving the estimate to guesswork.

Digital calipers, dial indicators, and CNC machine controllers all display measurements in decimal inches, not fractions. A machinist cutting a part to a blueprint dimension of 7/16 inch has to know the caliper will read 0.4375, not a fraction, before the cut passes inspection. CAD programs such as AutoCAD and SolidWorks store every dimension internally as a decimal and only format it as a fraction when a drawing calls for one. Construction and woodworking trades lean more on fractional callouts on a tape measure, which is why this page and the decimal to feet and inches converter exist side by side: one handles shop-floor decimal readings, the other handles tape-measure fractions.

Every fraction with a denominator of 2, 4, 8, 16, 32, or 64 converts to an exact, terminating decimal, because each denominator is a power of 2. A denominator like 3 or 10, such as 1/3 inch, produces a repeating decimal that never terminates, which is why fractional-inch tools only use halves through sixty-fourths. When rounding a long decimal back to a fraction, match the precision to the tool in hand: 1/16 inch for a tape measure, 1/32 inch for tighter woodworking joints, and 1/64 inch for machining. The fractional inch converter handles that rounding automatically at any of these four precisions.

Decimal inches and decimal feet are different units and get confused often. A value like 8.5 in decimal inches stays at 8.5 inches, but the same 8.5 read as decimal feet means 8.5 × 12 = 102 inches. If the number being converted actually represents feet, use the decimal feet to inches calculator instead, or check the relationship in the other direction with the inches to decimal feet converter. For background on precision, rounding, and how calipers display decimal inches, see the decimal inch measurement guide.

The most frequent error is forgetting to add the whole number back after converting the fraction, so 4 5/8 becomes 0.625 instead of 4.625. Another is rounding too early: when 1/64 inch precision is needed, rounding the fraction to 1/16 first and then converting throws away accuracy before it has been used. A third mistake is misreading a dual-marked ruler and mixing up an inch value with a millimeter one. This tool avoids all three by carrying the full decimal value through every step and only rounding once, at the final display, for the fraction result.