Centimeter ruler

What is a centimeter?

A centimeter is one hundredth of a meter — about the width of an adult fingertip. It sits in the sweet spot for everyday measuring: smaller than an inch (2.54 cm), larger than fiddly sub-millimeter units. Most of the world measures daily life in centimeters: heights, paper sizes, furniture, screen diagonals.

Reading the cm scale

In cm mode the long numbered ticks are centimeters — 1, 2, 3, and so on. Between each pair sit nine shorter ticks: millimeters. The medium-length tick halfway between is the half centimeter (5 mm). An object ending at the third short tick past 7 measures 7.3 cm. If you need the value purely in millimeters, switch to mm mode and read 73 mm directly.

Handy size references

Everyday objects, for sanity-checking your calibration or estimating without the ruler:

• Standard paperclip — about 3 cm long
• AA battery — about 5 cm long
• Credit / bank card — 8.56 cm wide (an exact standard, great for checking calibration)
• US penny — about 1.9 cm across
• Smartphone width — typically 7–8 cm

Conversions

From	To	Multiply by
cm	mm	10
cm	m	0.01
cm	inches	0.3937
inches	cm	2.54 (exact)

The inch conversion is exact by definition — one inch is defined as 2.54 cm — so switching the ruler between cm and inches never introduces rounding error in the tick positions themselves.

Frequently asked questions

How many millimeters are in a centimeter?

Ten. A centimeter is defined as exactly 10 millimeters, and the on-screen ruler shows this directly: ten small ticks between every pair of numbered centimeter marks.

How many inches is a centimeter?

One centimeter equals exactly 0.3937 inches (one inch is defined as exactly 2.54 cm). So 10 cm is about 3.94 inches — just under four inches.

What everyday objects are about one centimeter?

A standard pencil is about 0.7 cm across, a US penny is about 1.9 cm across, and the width of an adult fingertip is roughly 1.5–2 cm. A paperclip is about 3 cm long and a credit card is 8.56 cm wide.