Centimeters (cm)

What is a centimeter?

The centimeter (also spelled centimetre) is a metric unit of length equal to one hundredth of a meter. The prefix "centi-" means one hundredth, so 100 centimeters make a meter and 10 millimeters make a centimeter.

One centimeter is about the width of a fingernail or a standard pea, and 2.54 centimeters make exactly one inch. It is the everyday unit for measuring things that are too big for millimeters but too small for meters.

What centimeters are used for

• Body height and clothing sizes in metric countries (a person 175 cm tall)
• Rulers, school geometry and paper sizes (A4 is 21 × 29.7 cm)
• Screen and furniture dimensions outside the US
• Rainfall and snow depth in weather reports
• Medicine: wound sizes, baby length and head circumference

Centimeters in real life

• A standard pencil is about 19 cm long
• A credit card is 8.56 cm wide
• A typical adult hand span is 20–23 cm
• A newborn baby is about 50 cm long
• A US quarter coin is 2.43 cm across

One centimeter is about 1.7 grains of rice laid end to end, or about 20 grains of sand laid end to end, or about 33 dust mites laid end to end, or about 41% of the length of a US quarter (diameter).

History of the centimeter

The centimeter was created with the metric system in 1795. It was the base length unit of the CGS (centimeter–gram–second) system used throughout physics from the 1870s until SI replaced it in 1960, which is why many older scientific units, such as the dyne and the erg, are built on centimeters.