How to Convert Imperial to Metric

Updated July 20, 2017

The imperial system of measurement is a standard of units formalised by the British government while the metric system was created by France and forms the basis for the International System of Units. Most of the world uses the metric system, but in the United States and other areas influenced by Britain, the imperial system continues to influence everyday measurements including those for cooking and distances. As a consequence, you may have to convert from imperial to metric units. All you need is a list of conversion factors.

Find the unit you need to convert on an imperial-to-metric conversion chart. Conversion charts list the equivalent units in each system and the factors you need to convert them.

Confirm that the conversion factor is dimensionally appropriate. This means you cannot use a conversion factor for litres, which is a unit of volume, to convert inches to litres. For the basic units of length, volume and mass this is simple, but for more complicated units such as acceleration or pressure, you could accidentally use the wrong conversion factor.

Multiply the number of your imperial units by their metric measurement per unit. For example, 1 inch is equal to 2.54 centimetres. Therefore, to convert 12 inches to centimetres, multiply 12 inches by 2.54 centimetres per inch to get 30.48 centimetres.


Conversion factors are the result of careful measurements and comparisons of the different units in each system. You will get more accurate results using a reputable list of factors than attempting to measure the factors yourself.

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About the Author

Marty Simmons started writing professional reports for the environmental consulting industry in 2008. His online instructional articles specialize in science and education. Simmons has a Bachelor of Arts in geology from Kent State University.