Inch Fractions to MM
How to convert inch fractions to millimeters
- Type a size in inches as a fraction, such as 5/32 or 1 3/8, or as a decimal.
- Read it in millimeters and decimal inches. Or type millimeters to get the nearest fraction, rounded to the 64th, 32nd, 16th or 8th you choose.
- The chart below lists every 64th of an inch from 1/64 to 1 inch.
Frequently asked questions
How do I convert an inch fraction to mm?
Divide the top number by the bottom one and multiply by 25.4. 5/32 in is 5 ÷ 32 = 0.15625 in, and 0.15625 × 25.4 = 3.969 mm.
What fraction is closest to 4 mm?
4 mm is 0.1575 in. The nearest 64th is 10/64, which simplifies to 5/32 in (3.969 mm), 0.03 mm smaller.
Why are drill bits and wrenches sized in fractions?
US and older British tools are made in fractions of an inch, usually down to 1/64. A metric drill of almost the same size often works: 5/32 in is close to 4 mm, and 1/4 in (6.35 mm) to 6.5 mm.