National Physical Laboratory

How do I correct lengths to 20ºC? (FAQ - Length)

To correct a length to 20ºC you need to calculate the difference (DT) between the ambient temperature and 20ºC. This difference is then multiplied by the product of the length (L) of the item and the expansion coefficient (A).

i.e. correction = A x L x DT

As an example, if the length of a nominal 500 mm steel rod is measured at 23.7ºC to be 500.035 mm then its length at 20ºC is given by the following (assuming the expansion coefficient of steel is 11.7 parts per million per °C):

500.035 mm - (11.7x10-6 x 500.035 x (23.7 - 20)) mm = 500.013 mm

Last Updated: 25 Mar 2010
Created: 18 Jul 2007


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