Inch Conversion Table

This is the master inch conversion table used by machinists, woodworkers, and engineers. Every fractional inch from 1/64" to 1" appears with its exact decimal value and millimeter equivalent, all on one page.

The table is built from first principles: 1 inch equals exactly 25.4 millimeters. Each row is a power-of-2 fractional inch reduced by greatest common divisor to its simplest form, so you never see an unreduced fraction like 8/16 where 1/2 belongs.

For a single lookup rather than the full scale, the decimal to fraction calculator and millimeters to inches calculator return one result at a time along with the formula used to get there. This table is for when you need the whole scale at once, on one screen or one printed sheet.

Read across any row to convert between the three formats. Find your fraction in the left column, then read the matching decimal inch and millimeter values in the same row. If your measurement falls between two rows, pick the closest fractional inch; that is the same value a tape measure or ruler will show you.

For example, the row for 11/16" shows a decimal value of 0.6875" and a millimeter value of 17.4625 mm. The row above it, 5/8" (0.625", 15.875 mm), and the row below it, 3/4" (0.75", 19.05 mm), bracket every value in between. Any caliper reading from 0.594" to 0.719" rounds to the 11/16" mark on a standard tape measure.

For machining work where 1/64" is not precise enough, switch to decimal inches or millimeters directly; calipers, micrometers, and CNC controllers all take decimal or metric input rather than fractions.

Say a caliper reads 0.4375 inch and you need to know which mark on a tape measure it lines up with. Multiply the decimal by 64: 0.4375 × 64 = 28. The Greatest Common Divisor of 28 and 64 is 4, so 28/64 reduces to 7/16. Scan the table above to the 7/16" row and you will find the same decimal, 0.4375", and its millimeter equivalent, 11.1125 mm (0.4375 × 25.4).

Going the other direction, a metric drawing might call out 12 mm. Divide by 25.4 to get inches: 12 ÷ 25.4 = 0.47244 inch. The closest row in the 1/64" table is 30/64", which the GCD reduces to 15/32" (0.46875", 11.90625 mm), off from 12 mm by only about 0.09 mm. That small gap is exactly why precision machining specs are usually written in decimal inches or millimeters rather than fractions: a fractional tape measure simply cannot land on every possible metric value.

Most real jobs move through all three formats in a single afternoon. A drawing might dimension a part in millimeters, a machinist cuts stock using a decimal-reading digital caliper, and the same part gets marked with a fractional tape measure before it goes to a bandsaw. This table exists so none of those three groups has to convert by hand or guess.

Woodworkers lean on the fraction column because lumber, plywood, and hardware are still sold and marked in fractional inches; see the fractional inch converter for a single-value version of the same math. Machinists and toolmakers lean on the decimal and tolerance side of the job; the machinist decimal reference covers thousandths, tenths, and standard tolerance bands in more depth. Anyone working from an imported part or a metric fastener chart will want the millimeters to inches calculator or the drill size chart, both of which use the same 25.4 mm-per-inch constant as this table.