One thing I never noticed before but is obvious after a week with folks visiting the US for the first or second time: Our coins don't have numbers. That's got to be super confusing.

I know that you're supposed to use the sizes to differentiate, but it's super weird and unintuitive that a dime is smaller than a nickel but is worth more. I could never wrap my head around that as a kid.

dime (0.10 USD) / quarter (0.25) / half dollar (0.5) have consistent weight/value, and were mostly silver pre-1965. nickel (0.05) and penny (0.01) were less valuable metals and thus worth less. I'm struggling to think of a country where coin size strictly increases with value.

In India this used to be true with coin *weight* -- 25p was smaller than 50p was smaller than ₹1 was smaller than ₹2, and ₹5 was smaller than ₹1 but much heavier/thicker. Then they messed it up completely.

The UK sort of has this nice system where there are four types of coin appearance, each at two drastically different sizes. But they mess it up because the pairs are 0.01/0.02, 0.05/0.10, 0.20/0.50, and 1.0/2.0, when the values logically group as 1/2/5 10/20/50 1/2.