system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5  Why are the United States' coins and Canada's coins basically the same size, shape, and color?  What happened that the two countries decided this would be a good idea?

I have Googled this and can't find a reason.  I would love to know.  Help!
gpt
This is pure conjecture, but perhaps it is a relic of past times when the value of a coin was tied to the value of the metal used to make it.

Gold is the most valuable, so you could have a $5, $10, $20, etc coin, with the value determined by how much gold is in it.

Silver is less valuable, and in the US, quarters were silver until 1965.

For the smaller denominations, nickel or copper are used, these being metals of even lesser value.

I would imagine a couple hundred years ago when the US and Canada started making their coins, the amount and type of metal used to make a coin of a certain value would have been similar, so the size, shape and color of each coin is the same.

Now that it's all fiat money anyway, all the coins are made with less valuable materials, but the basic design of each coin has remained the same.