Decimeters to Millimeters (dm to mm)

1 decimeter equals 100 millimeters exactly.

1 decimeter = 100 millimeters

How to convert decimeters to millimeters

To convert decimeters to millimeters, multiply the number of decimeters by 100. This factor is exact. To go the other way, multiply millimeters by 0.01.

millimeters = decimeters × 100

Example: 10 decimeters = 1,000 millimeters.

About these units

Decimeter (dm)

Metric (SI)Current unit

One tenth of a meter (10 cm). Rarely used in everyday practice.

Deci, meaning a tenth, was among the prefixes of the first metric system, and Wikipedia's prefix table dates it to 1795. The decimeter (dm) is therefore 10 centimeters, 100 millimeters or about 3.937 inches. Of all the early metric multiples it is the one that shows up least in daily speech, since people reach for centimeters or meters instead.

Its real importance is as the edge of the liter. A liter is defined as one cubic decimeter, so a 10 cm cube holds exactly one liter. Between 1901 and 1964 the liter was defined through the kilogram instead, which made it very slightly different from the cubic decimeter. The unit also survives in a few specialist places. Chemists record the path length used for specific rotation in decimeters, and ship draught marks are given in decimeters in most of the world. A standard compact disc, at 120 mm, is 1.2 dm across.

1 decimeter = 0.1 meters (exactly).

Sources: Wikipedia: Decimetre; Wikipedia: Metric prefix; NIST: metric (SI) prefixes

Millimeter (mm)

Metric (SI)Current unit

One thousandth of a meter. Used in engineering, manufacturing and rainfall measurement.

Carl Friedrich Gauss put the millimeter at the base of his 1832 proposal for absolute units, pairing it with the milligram and the second, although the centimeter-based CGS system later won out among scientists. The name combines the metric prefix milli-, from the Latin for one thousand, with the meter. Since 1983 a millimeter has been tied to the speed of light: it is the distance light covers in 1/299,792,458,000 of a second.

Millimeters are the language of fine mechanical work. Standard rulers are divided into them, digital calipers commonly read to 0.01 mm, and mechanical pencil leads come in 0.5 and 0.7 mm. Copy paper is about 0.1 mm thick, and a thin hair, at 0.02 to 0.04 mm across, is close to the smallest thing the naked eye can see. A wave with a frequency of 300 GHz has a wavelength of 1 mm. An inch is exactly 25.4 mm. One trap for readers in the United States is that mil there traditionally means a thousandth of an inch, not a millimeter.

1 millimeter = 0.001 meters (exactly).

Sources: Wikipedia: Millimetre; Wikipedia: Centimetre-gram-second system of units; NIST Guide to the SI, Appendix B.8: conversion factors

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