MM to Inches Conversion Calculator
Convert millimeters to decimal inches and the nearest 1/16-inch fraction. Uses the exact definition: 1 inch = 25.4 mm. Also shows feet, cm and meters.
mm
Nearest 1/16 inch: 1"
- 1
Conversion factor
1 in = 25.4 mm - 2
Divide by factor
25.4 ÷ 25.4 = 1
How does this calculator work?
Divide mm by 25.4 to get inches: inches = mm ÷ 25.4. The inch is defined as exactly 25.4 mm — conversion is exact. The result also shows the nearest 1/16-inch fraction, plus feet (÷ 304.8), cm (÷ 10), and meters (÷ 1000).
Formula
How this is calculated
The inch is defined as exactly 25.4 millimeters under the international yard and pound agreement of 1959. This makes the mm-to-inches conversion exact: divide any millimeter value by 25.4 and you get the precise decimal equivalent with no rounding in the factor.
In practical use — construction, woodworking, manufacturing, and drafting — fractions of an inch are often preferred over decimals. The most common fractions are halves, quarters, eighths, and sixteenths of an inch. The calculator displays the nearest 1/16 inch (0.0625 in = 1.5875 mm) alongside the decimal result. For example, 20 mm / 25.4 = 0.7874 in, and the nearest 1/16 is 13/16" (0.8125 in, about 0.025 mm away).
For larger measurements, the result is also shown in feet (mm ÷ 304.8), centimeters (mm ÷ 10), and meters (mm ÷ 1000) so you can move between all common measurement systems in one step. All conversion factors are exact under their international definitions.
Frequently asked questions
1 inch = exactly 25.4 mm (by definition since 1959). To convert mm to inches, divide by 25.4. Examples: 50 mm = 1.969 in; 100 mm = 3.937 in; 300 mm = 11.811 in.
Divide mm by 25.4 to get decimal inches. Multiply the decimal part by 16 and round to get sixteenths. For 18 mm: 18/25.4 = 0.7087 in → 0.7087 × 16 ≈ 11.3 → nearest 11/16". This calculator shows the nearest 1/16 automatically.
2.54 is the centimeter-to-inch factor (1 cm = 0.01 m, so 1 in = 2.54 cm). Since 1 cm = 10 mm, one inch equals 10 × 2.54 = 25.4 mm. Both are exact under the same 1959 international definition.
Also known as
TG we-Calculate Editorial Team. (2026). MM to Inches Conversion Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/mm-to-inches-conversion-calculator
TG we-Calculate Editorial Team. "MM to Inches Conversion Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/mm-to-inches-conversion-calculator.
TG we-Calculate Editorial Team, "MM to Inches Conversion Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/mm-to-inches-conversion-calculator
@misc{wecalculate_mm_to_inches_conversion_calculator, title = {MM to Inches Conversion Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/mm-to-inches-conversion-calculator}}, year = {2026}, note = {TG we-Calculate} }
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