For example, take the 0-100 range in Fahrenheit. In Celsius it is -18 to +38 degrees.

My Dad was a swim coach for the YMCA and I spent many summers swimming for his teams. I enjoyed the competitive thrill of trying to beat my personal record for my breaststroke. Part of the trouble was knowing what my personal record was. In the Charlotte, North Carolina metro area there were many pools that were 25 yards long and others that were 25 meters. If I swam my best race in a 25 meter pool, should I just convert that to 25 yards? Or vice versa?

(Insert pic of me at the swimming pool).

The back and forth of trying to figure out if I should measure my PR on 25 yards, meters or convert between the two was a trivial matter in the grand scheme of things. However, the USA’s indecision on converting to the metric system has caused lots of friction on the world stage.

The US is on what is called the British Imperial System which has its origins back to Ancient Roman times. In the 1790s there were a lot of measurement units being used such as the Dutch, British and other regional units. There was little uniformity across the states. In 1793, then Secretary of State, Thomas Jefferson wrote his French friend Joseph Dombey to bring over some of the newfangled “French Metric” weights. Dombey boarded a ship with an official Kilogram and other metric weights, but on the way was captured by British pirates in the Carribean.

(Use one of the two above).

Jefferson got cold feet and worried about the cost of sending delegates back and forth to France to verify the measurements. Shortly after, the US decided to stick with the British Imperial System. America’s prowess in industry grew and all the machinery was codified in feet and inches and workers quickly grew accustomed to working in the imperial system. . There was also a bit of an American independence spirit to the metric system. The metric system seemed European and America wanted to lead not follow.

In 1965, Britain officially switched off of the British imperial system in favor of the metric system. Here is a map from the 1971.

(source)

Light brown shows all of the countries that were already on the metric system pre-WW2 and the dark brown countries that converted to metric post-WW2.