mmtoinches
Exact 25.4mm/inch standard

Convert millimeters to inches, precisely.

Type any value below for an instant, exact conversion — decimal and nearest fraction included. Built for engineering, sewing, jewelry, and hardware work where the last decimal place matters.

mm
0.39370 in

25/64" nearest 1/64 fraction  ·  formula: mm ÷ 25.4 = in

inches = mm ÷ 25.4

mm = inches × 25.4

1 inch defined as exactly 25.4mm — 1959 international yard & pound agreement

Reference

MM to Inches Chart

Common values, decimal & nearest fraction. Every row links to a full breakdown.

Millimeters Inches (decimal) Nearest fraction
For the workshop

MM to Inches Fractions

Tape measures and drill bits are marked in 1/16" or 1/64" increments, not decimals. Use this table to read off the mark you'll actually find on the tool.

1.5875 mm

1/16"

3.175 mm

1/8"

6.35 mm

1/4"

9.525 mm

3/8"

12.7 mm

1/2"

15.875 mm

5/8"

19.05 mm

3/4"

25.4 mm

1"

Where it's used

Built for the moment you need it

Engineering & CAD

Verify drawing dimensions when switching between metric and imperial unit settings. Results to 5 decimal places.

Sewing & fabric

Convert pattern measurements to the inch marks on a US tape measure or ruler, fraction-accurate.

Bolts & hardware

Cross-check metric bolt and socket sizes against SAE wrenches before you're stuck under the car.

Questions

Frequently asked

How do I convert mm to inches?
Divide the millimeter value by 25.4. For example, 50 mm ÷ 25.4 = 1.9685 inches.
How many inches is 10 mm?
10 mm equals 0.3937 inches, or approximately 25/64 of an inch.
What is the exact mm to inches conversion factor?
1 inch is defined as exactly 25.4 millimeters under the 1959 international yard and pound agreement — an exact figure, not a rounded approximation.
Can I convert mm to inches without a calculator?
Rough mental estimate: divide by 25 instead of 25.4, then subtract about 1.5%. For precise work, always use the exact 25.4 divisor.
Is this accurate enough for engineering or CAD work?
Yes — results use the exact 25.4mm/inch factor to 5 decimal places. For final production drawings, always verify against your CAD software's native unit settings.