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Units

Centimetres, millimetres and inches

Millimetres, centimetres and inches for short lengths.

Calculated in this page. Nothing you type is sent to a server.

Millimetres25.4
Centimetres2.54
Inches1

One inch is exactly 25.4 mm, so 2.54 cm. Ten millimetres are one centimetre. Fabric, a phone width and a ring diameter all use this same inch. Screen sizes advertised in inches are the diagonal, which is a different question from the width of a piece of cloth.

The factor is exact. The figure on screen is rounded for reading.

How to use it

  1. Enter millimetres, centimetres or inches.
  2. Read the other two. An inch is 25.4 mm.
  3. For a person’s height, use the height page. For a ring, use the ring page.

The exact inch

One inch is exactly 25.4 millimetres, which is 2.54 centimetres. Ten millimetres are one centimetre. A 30 cm ruler is 300 mm and 11.81 inches. The page uses those factors and rounds the display.

Small hardware, a phone width, a picture frame and a hem are this conversion. Standing height has its own page because it is usually said in feet as well as inches. A ring is usually a diameter or a letter, and the ring converter already divides circumference by π.

What people mix up

A screen sold as 14 inches is the diagonal of the display, not the width of the laptop. Converting that 14 to 35.6 cm is correct for the diagonal and misleading if you needed the width.

Fabric widths in inches and pattern measurements in centimetres meet on this page. Keep one system inside a single cut. The height converter is the one to use for feet and inches together.

Questions

How many millimetres in an inch?

Exactly 25.4 mm.

How many centimetres in an inch?

2.54 cm.

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