UnitConvConvert
Length

Convert inches to millimeters

1 in=25.4mm

Use the converter below to change any inches value into millimeters instantly — with formula, conversion table, and real-world examples.

25.4

Conversion formula

Forward
millimeters = inches × 25.4
Reverse
inches = millimeters × 0.03937

Example: 10 in × 25.4 = 254 mm.

About both units

From

Inch

in

The inch equals 2.54 centimeters exactly since 1959. It is the global standard for screen diagonal sizes — a "55-inch TV" has a 139.7 cm diagonal. Pipe diameters, US and UK shoe sizes, and hard-drive form factors are all specified in inches. 1 inch = 1/12 foot = 1/36 yard.

Real-world: A 65-inch TV has a 165 cm diagonal. A smartphone screen is typically 6–7 inches. Standard copper plumbing in the UK is ½ inch or ¾ inch.
Read full inch reference →
To

Millimeter

mm

The millimeter equals one thousandth of a meter and is essential in precision engineering, manufacturing and rainfall measurement. A 10-millimetre rainfall is a moderate shower; over 50 mm in a day is classified as heavy. Machined parts, screws and PCB dimensions are all given in mm.

Real-world: A 2 euro coin is 25.75 mm across and 2.2 mm thick. Rainfall of 50 mm in 24 h is a red-warning event in most of Europe.
Read full millimeter reference →

Inch to Millimeter conversion table

Common inches to millimeters values for quick reference.

Inch (in)Millimeter (mm)
1 in25.4 mm
5 in127 mm
10 in254 mm
25 in635 mm
50 in1,270 mm
100 in2,540 mm
250 in6,350 mm
500 in12,700 mm
1,000 in25,400 mm
5,000 in127,000 mm

Tips & common mistakes

Quick tips

  • 1 inch = 2.54 cm exactly by international agreement — no rounding.
  • Screen sizes are always diagonal, never width. A 27-inch monitor is about 60 cm wide.
  • To convert cm to inches mentally, divide by 2.5 and subtract 1.6%.

Avoid these

  • Reading a screen size as width. A 65-inch TV is about 143 cm wide — the 165 cm figure is diagonal.
  • Using 2.5 instead of 2.54 on precision drawings — the 1.6% error matters in manufacturing.
  • Confusing inches of length with inches of mercury (inHg) — a pressure unit, not length.

Frequently asked questions

How many millimeters in a inch?
One inch equals 25.4 millimeters.
How do I convert inches to millimeters?
Multiply the inch value by 25.4 to get the equivalent in millimeters.
What is 100 inches in millimeters?
100 inches equals 2,540 millimeters.
Is a inch bigger than a millimeter?
Yes. 1 inch equals 25.4 millimeters, so one inch is larger.
How to convert inches to millimeters without a calculator?
Multiply by 25.4 for a quick estimate; use a calculator for precise results.

Related length conversions

📊 See full comparison matrix →

More from Inch

in → m
1 = 0.0254 m
in → km
1 = 2.5400e-5 km
in → cm
1 = 2.54 cm
in → mi
1 = 1.5783e-5 mi
in → yd
1 = 0.02778 yd
in → ft
1 = 0.08333 ft
in → nmi
1 = 1.3715e-5 nmi
in → µm
1 = 25,400 µm

More to Millimeter

m → mm
1 = 1,000 mm
km → mm
1 = 1,000,000 mm
cm → mm
1 = 10 mm
mi → mm
1 = 1,609,344 mm
yd → mm
1 = 914.4 mm
ft → mm
1 = 304.8 mm
nmi → mm
1 = 1,852,000 mm
µm → mm
1 = 0.001 mm

Conversions in other categories

WeightKilogram → PoundTemperatureCelsius → FahrenheitVolumeLiter → US GallonAreaSquare Meter → Square FootSpeedKilometer per Hour → Mile per HourEnergyKilojoule → KilocaloriePressureBar → Pound per Square InchPowerKilowatt → Mechanical Horsepower