Convert meters to millimeters

The meter is an SI base unit and the reference point for every other measure of length. Since 1983 its value has rested on the speed of light: the meter is the distance light travels in vacuum in 1/299,792,458 of a second[1]. Before that the standard was a platinum-iridium bar kept near Paris, and for twenty-three years from 1960 the wavelength of light from krypton-86[1].

A millimeter comes from dividing that meter into a thousand equal parts. The prefix says so on its own: milli- means one thousandth in the SI system[2], so one millimeter is 0.001 meters and the symbol for the unit is mm. Beyond length the same prefix marks off thousandths of other quantities as well: in mass it gives the milligram, in volume the milliliter.

The millimeter matches the smallest graduation you see on an ordinary ruler and on a tape measure. That is why a dimension gets measured in meters and written in millimeters wherever precision counts: on a workshop drawing, in a model for three-dimensional printing and in an order for cut-to-size material.

A meter contains 1,000 millimeters. To turn meters into millimeters you multiply by a thousand: 2.4 m gives 2,400 mm.

In decimal writing it is enough to move the point three places to the right. A value of 0.5 m becomes 500 mm that way. A value of 12 m gives 12,000 mm, because a whole number simply picks up three zeros.

The field at the top of the page does the same arithmetic while you type. It also works the other way round: a number entered on the millimeter side shows up straight away as meters.

The formula has one shape: millimeters = meters × 1000. The same arithmetic can be written as dividing by 0.001, because multiplying by a thousand and dividing by one thousandth lead to the same number.

Take a room height of 2.7 m. Multiply 2.7 by 1,000 and you get 2,700 mm. Values with more decimal places behave the same way: 9.144 m gives 9,144 mm, which is exactly ten yards.

A drawing runs in one unit, and the standard lets that unit be stated once, on the drawing or in an associated document, and left out of the individual dimensions[3]. When that unit is the millimeter, a dimension measured in meters has to be converted into it so the whole set of documentation speaks one measure.

The same dimension reads in centimeters on the meters to centimeters converter. The way back is on the millimeters to meters converter. A route given in kilometers turns into millimeters on the kilometers to millimeters converter, where the multiplier grows from a thousand to a million.