And in the "pedantic++" category: check out flag proportions, too. See for example https://flagspot.net/flags/nl-lu.html, which explains the difference between the flags of Monaco and Indonesia (buried in a discussion about the flags of the Netherlands and Luxembourg): same colors, but different proportions.

So, Belgium should be 13:15 (https://flagspot.net/flags/be.html, for US flags 10:19 seems best for all uses (https://flagspot.net/flags/us-size.html#prop), etc.

But that certainly is just a fyi :)