A decimeter (dm) is a unit of length in the International System of Units equal to 0.1 meters. It is also referred to as a decimetre outside of the US.

What is a decimeter

A decimeter is a metric measurement of length. It is a submultiple of the meter, the SI base unit of length.

Decimeter definition

A decimeter is defined in terms of the meter. The prefix "deci-" indicates that a decimeter is a submultiple of a meter; specifically, a decimeter is 1/10 of a meter. In other words, there are 0.1 meters in 1 decimeter, or 10 decimeters in 1 meter.

1 decimeter = 0.1 meters

The meter is formally defined as the length of the path traveled by light in a vacuum in of a second.

How long is a decimeter

Below are a few examples of commonly used units of length relative to the decimeter.

Metric prefixes

In the International System of Units, prefixes are used to denote multiples or submultiples of a base unit (discussed below). All units measuring the same quantity are related to each other by powers of 10. For example, the base unit of length in the SI is the meter. A decimeter is related to a meter by its prefix "deci-" which indicates that it is 1/10 smaller than the base unit, which in this case is the meter. Thus, a decimeter is 0.1 meters. All SI units use the same system of prefixes making the system very easy and convenient to use, which is why it is the most widely used measurement system in the world. The figure below shows some of the metric prefixes and how they are related to each other by powers of 10 using the quantity of length as an example:

Why we use the metric system

The main reason we use the International System of Units, the modern form of the metric system, is because of its ease of use and neutrality. It was developed with the goal of standardizing units of measurement worldwide since too many different systems existed at the time. The SI enables us to very easily choose units of measurement that are appropriate in magnitude since all units that measure the same quantity are related by some power of 10 indicated by SI prefixes.

In contrast, while it is also possible to pick measurements of length that are appropriate for the given situation in the US customary system of units, it is also more tedious, since converting between these units requires knowledge of the conversion factors. In SI, all units of measurement are related by some power of 10, so it is only necessary to shift the decimal place. In most other systems of measurement, various units are used to measure the same attribute, and these units typically are not related by a constant power (as they are in SI).

In the US customary system of measurement for example, inches, feet, yards, and miles are commonly used units of length, all of which are related by different factors. There are 12 inches in 1 foot, 3 feet in 1 yard, and 1760 yards in 1 mile. Even knowing these conversion factors, it is still more tedious to convert between the various lengths than simply counting decimal places in SI. Also, none of these conversion factors apply to other units of measurement in the US customary system, while SI prefixes can be applied to any SI base unit.

Why the size of the unit matters

It is important to choose an appropriate unit of measurement for the given application. For example, if someone were measuring the diameter of a plate, the choice of decimeters as the unit of length would be reasonable. The result would likely be some number in the 10-30 dm range. Measuring the plate in megameters (103) however, would not be a particularly reasonable choice, since 10 dm = 0.000001 Mm. The measurement 0.000001 Mm would be difficult for most people to conceptualize, and would therefore not be particularly useful.

The ability to express various units of measurement in different magnitudes (powers of ten) simply by changing the prefix on the base unit is a major advantage of SI compared to many other systems of measurement.