MM to inches converter

inches = mm ÷ 25.4. One inch is exactly 25.4 millimeters by international definition, so the only rounding is in the result.

Example: 19 mm ÷ 25.4 = 0.748 in, almost exactly 3/4 in (0.75 in). That's why a 19 mm wrench is a close substitute for a 3/4-inch one, though not a perfect fit.

The fraction is the nearest one, not an exact match. 6 mm is closer to 15/64 than to 1/4 in; on a 1/16 tape it reads as 1/4.

Many metric sizes sit close to an inch fraction, but close isn't the same. A 10 mm socket is 0.394 in, while 3/8 in is 0.375 in: the inch socket won't fit a 10 mm nut, and the 10 mm socket will slip on a 3/8-inch bolt head and can round it off. For drill bits a near size is often fine for wood, but for tapped holes, bearings and press fits use the specified size. When in doubt, measure with calipers set to millimeters.

Engineering drawings, machinists and 3D-printing software usually work in decimal inches (thousandths). Woodworkers, carpenters and sewing patterns use fractions on a tape measure. The converter shows both: choose the number of decimal places for the decimal result, and 1/16 or 1/64 for the fraction.

To go the other way, the inches to mm converter accepts fractions such as 5/16 or 1 1/4.

• 25 mm is about 1 inch (0.984 in), so mm ÷ 25 gives a fast estimate.
• 1 mm is about 1/25 of an inch, a little more than 1/32 in.
• Paper and screens: 210 mm (the width of A4 paper) is 8.27 in, a bit narrower than US Letter's 8.5 in.

The value you type is saved in the page link; use Share to send the exact conversion.

To go the other way, use the inches to mm converter. For centimeters, try the cm to inches converter.