Unit Conversion

What is Millimeter – Definition & Conversion


To measure the length of the very small objects less than a centimeter, a millimeter is a suitable unit. The millimeter with abbreviation as mm is a unit of displacement or distance for a small object.

The mm is equivalent to 0.001 meters. Also, there are about 25.4 millimeters in one linear inch. In this topic, the student will learn about millimeters and their conversions.

Definition of Millimeter

The millimeter is a unit of length in the metric system, equivalent to one-thousandth of a meter (the SI base unit of length). In the standard metric system, power-of-10 prefix multipliers facilitate the derivation of other.

Formally, one millimeter is the distance travelled by a ray of electromagnetic (EM) energy through a vacuum in a time span of 3.33564095 x 10-12 seconds.

Thus, the millimeter and its kin are also used to specify the wavelengths of electromagnetic fields, especially at ultra-high and microwave radio frequencies.

Further, such radio spectrum occupies an informally defined range of wavelengths from roughly 1 mm to several tens of kilometers. The speed of EM-field propagation in a vacuum is 2.99792458 x 1011 millimeters per second.

One simple way to measure the centimeter is by using everyday objects that are close to 1 centimeter in size, like a pencil, pen or highlighter. Millimeter gives more precision value to such small objects.

Moreover, a millimeter is a unit of length in the metric system which is equal to \(\frac{1}{1000} th of a meter.

1 mm is equivalent to 0.039370 inches.


History of a Millimeter

The metric system of weights and measures was defined and adopted in France in 1795. John Wilkins was the first person to publicly recognize the need for universal length measurement.

So as to carry out a measurement locally to avoid having to have a definition that refers to a stored reference unit.

Thus, he proposed using the length of a “second’s pendulum” which made half an oscillation per second. But later, it was found that there is a slight difference in this length around the world.

Therefore, the Academy of Sciences devised a new measure, 1/10000000 of the distance from the Equator to the North Pole.

Moreover, they put to use the new value to create a metal bar that stores at the BIPM’s headquarters and known as “international prototype meter”. This standard has since been superseded and further defined the meter as “1650763.73 wavelengths of the orange-red emission line of a krypton-86 atom in a vacuum”.

Most recently, in 1983, the meter defines as “the distance travelled by light in a vacuum in 1/299792458 of a second”. From this, we derive the centimeter as the distance travelled by light in a vacuum in 1/2997924580 of a second.

Millimeter Conversions

One inch equals 25.4 millimeters, but this value is not constant, so we need a special conversion factor. Also, to obtain a centimeter measurement from feet, divide the original measurement by 0.032808. And, to get centimeters from yards, divide the original measurement by 0.010936.

Also, 1 cm = 10 mm (millimeters)

  • 1 micrometer i.e. µm or µ = 0.001 (10-3) mm.
  • 1 nanometer (nm) = 10-6 cm.
  • 10 decimeter = 1 meter
  • 1 Angström unit (Ä) = 10-7 cm
  • 10 millimeter = 1 centimeter
  • 1000 millimeter = 1 meter
  • 10 meter = 1 decimeter
  • 10 decimeter = 1 hectometer
  • 1000 meter = 1 kilometer
  • 10 hectometer = 1 kilometer

Solved Question for you

Q: Convert the following measurements into mm.

  1. 145 cm
  2. 5.6 m
  3. 3.7 km

Ans: (a) 145 cm x 10 =  1450 mm

(b) 5.6 m x 1000 = 5600 m

(c) 3.7 km x 106 = 3.7 x 106 mm

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