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Decimeter — Definition, Formula & Examples

A decimeter (dm) is a unit of length in the metric system equal to one-tenth of a meter. That makes it exactly 10 centimeters, or about the width of an adult's fist.

The decimeter is a metric unit of length defined as 10−110^{-1} meters. It occupies the position between the centimeter (10−210^{-2} m) and the meter (10010^{0} m) in the base-10 hierarchy of metric length units, with the symbol dm.

Key Formula

1 dm=0.1 m=10 cm=100 mm1 \text{ dm} = 0.1 \text{ m} = 10 \text{ cm} = 100 \text{ mm}
Where:
  • dm\text{dm} = decimeter, the unit being converted
  • m\text{m} = meter, the base unit of length in the metric system
  • cm\text{cm} = centimeter, one-hundredth of a meter
  • mm\text{mm} = millimeter, one-thousandth of a meter

How It Works

To convert between decimeters and other metric lengths, you move the decimal point. Since 1 dm = 0.1 m, multiply decimeters by 0.1 to get meters. Since 1 dm = 10 cm, multiply decimeters by 10 to get centimeters. For millimeters, multiply decimeters by 100, because 1 dm = 100 mm.

Worked Example

Problem: A ribbon is 35 centimeters long. How many decimeters is that?
Set up the conversion: Since 1 dm = 10 cm, divide the number of centimeters by 10.
35 cm÷10=3.5 dm35 \text{ cm} \div 10 = 3.5 \text{ dm}
Answer: The ribbon is 3.5 dm long.

Visualization

Why It Matters

Decimeters appear often in science classes when measuring volumes, because 1 cubic decimeter equals exactly 1 liter. Understanding decimeters also strengthens your grasp of how the metric system scales by powers of ten.

Common Mistakes

Mistake: Confusing "deci-" (one-tenth) with "deca-" (ten), and thinking a decimeter is 10 meters.
Correction: The prefix "deci-" means one-tenth. A decimeter is 0.1 meters, not 10 meters. The prefix for ten is "deca-" (as in decameter).

Related Terms