A centimeter is a metric unit of length equal to one hundredth of a meter, about the width of a fingernail. Its symbol is cm. There are 100 centimeters in 1 meter and 10 millimeters in 1 centimeter, and 1 inch equals 2.54 centimeters.
Each numbered mark on a centimeter ruler is 1 cm apart, and the 10 small spaces between them are millimeters. Line the object up with 0, then read where it ends.
Formal definition and notation
The centimeter is the unit of length formed from the SI base unit, the meter, with the prefix centi-, which means 10−2, or one hundredth. So 1 cm = 0.01 m, and 1 m = 100 cm. The prefix centi means one hundredth, the same rule that makes a cent one hundredth of a dollar.
Symbol
Read it as
Meaning
cm
centimeter(s)
the symbol; it has no period and no s in the plural: 5 cm
A meter is 100 times longer than a centimeter: about the height of a kitchen counter. A centimeter is about a fingernail’s width.
Centimetervs.Millimeter
A millimeter is 10 times shorter than a centimeter: the smallest marks on a metric ruler. 1 cm = 10 mm.
Centimetervs.Inch
An inch is a customary (US) unit, about 2.5 times as long as a centimeter: 1 in = 2.54 cm.
Quick check: 3 questions
Question 1 of 3
How many centimeters are in 2 meters?
Show answer and explanation
Answer: B.2 × 100 = 200. Choice A multiplies by 10 (that would be decimeters), choice C by 1,000 (millimeters), and choice D divides when it should multiply.
Question 2 of 3
450 centimeters is how many meters?
Show answer and explanation
Answer: D. Divide by 100 to go to the larger unit: 450 ÷ 100 = 4.5. Choice A divides by 10, choice B by 1,000, and choice C multiplies instead.
Question 3 of 3
Which length is closest to 1 centimeter?
Show answer and explanation
Answer: C. A fingernail is about 1 cm wide. A new pencil is about 19 cm, a door is about 200 cm tall, and a car is roughly 450 cm long.
Centimeter: frequently asked questions
How many centimeters are in an inch?
One inch is 2.54 centimeters. To change inches to centimeters, multiply by 2.54: a 10-inch tablet screen is 10 × 2.54 = 25.4 cm. To change centimeters to inches, divide by 2.54: 30 cm is about 11.8 inches. A quick estimate is that 1 inch is about 2.5 cm.
How big is 1 centimeter?
About the width of a fingernail, the thickness of a pencil, or the width of a standard paper clip. On a ruler it is the space between two numbered marks on the metric side. Ten of them laid end to end make 10 cm, about the length of a crayon or the width of a palm.
Is centimeter spelled centimetre?
Both spellings name the same unit. Centimeter is the American spelling used in US schools and tests; centimetre is the British spelling used in many other countries. The symbol is cm either way, written with no period and no s: 1 cm, 5 cm.
LengthLength is how long something is: the distance from one end of an object to the other. You measure it by counting equal units laid end to end with no gaps or overlaps, such as inches, feet, centimeters or meters. A new pencil is about 7 inches long.Measurement · Grade 1, Grade 2, Grade 3MeterA meter (m) is a metric unit of length equal to 100 centimeters. It is the base unit of length in the metric system, a little over three feet (about 3.28 feet). A doorway is about 2 meters tall, and 1,000 meters make a kilometer. To change meters to centimeters, multiply by 100.Measurement · Grade 3, Grade 4, Grade 5PeriodThe period of a repeating function is the horizontal length of one complete cycle: the smallest distance after which the graph repeats exactly. y = sinx and y = cosx have period 2π, or 360°, and y = tanx has period π. For y = sin(Bx) or y = cos(Bx), the period is 2π|B|.Trigonometry · Algebra 2, PrecalculusSquareA square is a quadrilateral with four equal sides and four right angles. It is a special rectangle and a special rhombus at the same time. For a square with side s, the perimeter is 4s, the area is s2, and each diagonal is s√2.Geometry · Kindergarten, Grade 2, Grade 3SideA side is one of the straight line segments that form the outline of a polygon. Two sides meet at each corner, or vertex. A triangle has 3 sides and a square has 4, and adding the lengths of all the sides gives the perimeter.Geometry · Kindergarten, Grade 1, Grade 2VolumeVolume measures the amount of space inside a three-dimensional figure, in cubic units such as cubic centimeters or cubic feet. You can find it by counting the unit cubes that fill the solid. For a rectangular prism, V = l × w × h; for any prism, it equals the area of the base multiplied by the height.Geometry · Grade 5, Grade 6, Grade 7Equal ToEqual to means having exactly the same value or amount, and it is written with the symbol =. Numbers that look different can still be equal to each other: 12 is equal to 0.5. When two amounts are not the same, one is greater than or less than the other.Symbols and Notation · Kindergarten, Grade 1, Grade 2KilometerA kilometer (km) is a metric unit of length equal to 1,000 meters, roughly six tenths of a mile. It measures long distances, such as the length of a road race or the distance between towns. To change kilometers to meters, multiply by 1,000: 3 km is 3,000 m.Measurement · Grade 4, Grade 5, Grade 6InchAn inch is a US customary unit of length equal to one twelfth of a foot, about the width of an adult thumb. Its abbreviation is in. Rulers split each inch into halves, quarters, eighths and sixteenths. One inch is exactly 2.54 centimeters, and 12 inches make 1 foot.Measurement · Grade 2, Grade 3, Grade 4HeightHeight is how tall something is: the distance from its bottom to its top, measured straight up and down. In geometry, the height of a shape is the perpendicular distance from a base to the opposite vertex or side, so it always meets the base at a right angle. Area and volume formulas use it.Measurement · Grade 2, Grade 5, Grade 6NumberA number is an amount or value used to count, measure, order and compare. We write numbers with digits (7), words (seven) or other symbols, but the number itself is the amount: 7 dots, the word seven and the numeral 7 all show the same number. Numbers include whole numbers, fractions, decimals and negatives.Number System · Kindergarten, Grade 1, Grade 2Decimal PointA decimal point is the dot that separates the whole-number part of a number from its fractional part. Digits to its left are ones, tens and hundreds; digits to its right are tenths, hundredths and thousandths. In 46.25 the point sits between 6 ones and 2 tenths, and you read it aloud as “and”.Number System · Grade 4, Grade 5, Grade 6PerimeterPerimeter is the total distance around a two-dimensional shape. To find it, add the lengths of all the sides. A rectangle with sides 5 and 3 has perimeter 5 + 3 + 5 + 3 = 16. Perimeter is a length, so it uses length units such as inches or meters, never square units.Geometry · Grade 3, Grade 4, Grade 5Metric SystemThe metric system is a system of measurement in which units are related by powers of 10. Its base units are the meter for length, the gram for mass and the liter for capacity. Prefixes name larger and smaller units: kilo- means 1,000, centi- means one hundredth and milli- means one thousandth, so 1 km = 1,000 m.Measurement · Grade 4, Grade 5, Grade 6Unit ConversionUnit conversion is rewriting a measurement in a different unit without changing the amount, such as writing 3 feet as 36 inches. You multiply by a conversion factor, a fraction equal to 1 such as 12 in1 ft. Converting to a smaller unit gives a larger number; converting to a larger unit gives a smaller number.Measurement · Grade 4, Grade 5, Grade 6WidthWidth is the distance across a shape or object from side to side. In a rectangle, width is one of the two side measurements used with length, usually the shorter one, and multiplying length by width gives the area of a rectangle. Width is measured in length units such as inches, feet, centimeters or meters.Measurement · Grade 3, Grade 4, Grade 5