UNIT CONVERTER / mm ↔ Inch Converter

mm ↔ Inch Converter

Convert millimeters and inches in both directions, including a fraction rounded to the nearest 1/64 inch.

Inputs

Updates as you type

Value to convert

Results

Decimal places

inch

1inch

Results
mm	25.4 mm
Fractional inch · nearest 1/64	1 inch

Overview

Convert millimeters and inches in both directions, including a fraction rounded to the nearest 1/64 inch.

Formula

inch = mm/25.4
mm = inch × 25.4
Fraction approximation = round(inch × 64)/64

Example

12.7 mm = 0.5 inch = 1/2 inch. 25.4 mm = 1 inch. A value of 1.999 inch rounds to 2 inches at the 1/64 increment.

How to use

Check the units, enter the required values and select the available calculation options.
Results update immediately. Correct any highlighted input before using the result.
Choose display precision, copy the result or share the current inputs. Reset restores the example values.

Engineering notes

The international inch is exactly 25.4 mm. The displayed fraction is approximate unless the input is an exact supported fraction.
Fraction rounding can differ by up to 1/128 inch. Enter decimal numbers: use 0.5 rather than 1/2.

Frequently asked questions FAQ

Does every millimeter value have an exact fractional inch equivalent?

No. Check the decimal inch result and your drawing tolerance before using the rounded fraction for fabrication.

Does display precision change the calculation?

No. Rounding is applied only to displayed results, not intermediate calculations. Small nonzero values use scientific notation. Consider the precision of the original measurements when interpreting results.