Measurement Blog
Longer reads on how units are defined, why they differ between countries, and where old measures survive.
The 2019 SI Redefinition: How the Kilogram Lost Its Cylinder
On 20 May 2019 the kilogram, ampere, kelvin and mole were redefined by fixing constants of nature. Here is what changed and why.
Why the US Gallon Is Smaller Than the Imperial GallonThe US gallon is 3.785411784 litres and the imperial gallon 4.54609 litres. The gap goes back to the reign of Queen Anne.
How the Inch Became Exactly 25.4 MillimetresUntil 1959 the British and American inches differed slightly. The international yard and pound agreement fixed both, and left the US survey foot behind.
Traditional Units That Refuse to DisappearFrom Japanese tsubo to the South Asian tola and the stone in Britain, old units survive in markets, trades and everyday speech long after metrication.