Why charts disagree
Each country runs its own sizing tradition: the US uses lettered sizes for tops and integer numbers for shoes; the UK uses smaller numbers for tops; the EU uses chest circumference in centimetres; Japan uses foot length in centimetres for shoes. On top of that, every brand cuts slightly differently — a US M from one brand can run small or large compared to another.
Use these charts as a starting point, then verify against the brand's published guide for high-value purchases.