Some trivia for you:
Q: When did the US start using the imperial system (inches, feet, yards, gallons, etc.), and why?
A: Prior to 1965, even the UK was on the…imperial system. The metric system wasn’t even official in the UK until just 54 years ago. The US didn’t change on this. The rest of the world did.
When global trade started becoming more common, there came a desire for a worldwide standard. France proposed the first metric system in 1790, which was met with considerable resistance. Belgium, Netherlands, and Luxembourg were the first to require its used in 1820, and France followed the mandate in 1837. The alternative was the imperial system, which was too closely associated with Britain to be palatable.
In 1875, most industrialized nations, excluding Britain but including the US, signed the Treaty of the Metre. The definition of a metre has changed over time, though, and a lot more recently than most people realized.
Initially, the definition was one-ten-millionth of the distance between the equator and the north pole. You might see the problem with this. The earth isn’t entirely spherical. So which ten-millionth? For which starting point? Thanks, France.
In 1983, the definition moved away from geographical distance to using lightwaves. As far as we know, light travels at the same speed, or some such nonsense that will be debunked a few centuries from now, as everything seems to be.
It had been changed in the meantime between 1791, when the first meter was officially set, and 1983, when it was set at its current length, the most recent prior it 1983 being 1960. The 17th Conférence Générale des Poids et Mesures now defines a meter as:
The weight of the kilogram has also changed over time, including in the past few months, but I don’t work in weight, making this really irrelevant, though still interesting. Here is a starting point for your own research on this, and how there are three keys kept in separate locations that all must be brought together to access the official kilogram, which is a physical object kept under a series of bell jars, Whoville-style.