Length converter

Millimeters to inches.

Turn a metric measurement into decimal inches and a usable ruler fraction. See how much precision you lose when rounding to a tick mark.

Millimeters (mm)Inch fraction precision

25.4 mm = 1 in

Nearest inch fraction≈ 1 in

Fraction rounding difference+0 mm

Metric length25.4 mm

Feet and inches0 ft 1 in

The marker shows the fractional part of one inch. This diagram illustrates tick positions; it is not a physical-size ruler.

Reverse conversion ↔Measure on screen ↗

Conversion formula

inches = millimeters ÷ 25.4

Enter the source length above. The result updates immediately. These calculations use exact length definitions: 1 m = 100 cm = 1000 mm, 1 in = 25.4 mm, and 1 ft = 12 in. Only the displayed answer and fractional ruler mark are rounded. The feet-and-inches output splits a length into whole feet and remaining inches; decimal feet do not encode an inch count.

Worked example

A 6 mm part is 0.23622 inches. The nearest 1/16-inch mark is 1/4 inch, which is 6.35 mm—0.35 mm longer than the original. For a tight-fitting part, keep the decimal or metric value rather than treating the fraction as exact.

Conversion table: mm → in

Select a source value to load it into the calculator. Decimal results are displayed to at most six places; inch fractions in this table are rounded to 1/16 inch.

Millimeters → Inches
Millimeters (mm)	Inches (in)	Nearest inch fraction
	0.03937	≈ 1/16 in
	0.11811	≈ 1/8 in
	0.19685	≈ 3/16 in
	0.23622	≈ 1/4 in
	0.314961	≈ 5/16 in
	0.393701	≈ 3/8 in
	0.472441	≈ 1/2 in
	0.787402	≈ 13/16 in
	1	≈ 1 in
	1.181102	≈ 1 3/16 in
	1.968504	≈ 1 15/16 in
	3.937008	≈ 3 15/16 in
	12	≈ 12 in

When to use this conversion

Use this when a metric screw, drill bit, craft component, or small part has to be compared with an inch ruler. Size conversion does not establish mechanical compatibility: thread pitch, diameter tolerances, and material still matter.

Choose 1/32 or 1/64 if your physical ruler supports finer divisions. More decimal places do not improve the accuracy of an original measurement.

Exact conversion versus a ruler reading

The unit relationship is exact, but a measured object may have uncertainty. At 1/16 inch, the maximum rounding difference is half a tick: 1/32 inch, or 0.79375 mm. The calculator shows the actual rounding difference for your value. Use a finer division only if the source measurement and physical instrument support that precision.

Next steps

Numerical conversion needs no display calibration. Comparing a physical object against your screen does. Use the ruler for small objects, a verified paper ruler away from your display, or an appropriate calibrated instrument for safety-critical measurements.

Measure on screen Printable ruler PDFs Screen calibration guide How to read a ruler

Related converters

Inches to millimeters.Convert a decimal, fraction, or mixed inch measurement into millimeters. No need to turn 2 3/8 into a decimal first.Centimeters to inches.Read the decimal answer, find its nearest inch-ruler mark, and keep the rounding difference visible.Millimeters to centimeters.Express small metric measurements in centimeters while preserving their millimeter detail.Millimeters to meters.Turn a detailed drawing dimension into a room-scale length while keeping every millimeter in the calculation.Meters to inches.Translate a metric length into decimal inches, then choose a fractional tick only if the job permits rounding.

Length converters ↗

Reference: NIST unit conversion factors. Calculations use the international foot, not historical survey-foot units. Fractions are explicitly approximate. NIST ↗