my foot is like 27 cm, what’s that got to do with the US/UK foot? i know how tall i am, i know how much less that is than 2m, so i know what a meter is at that scale. for smaller scales? you know how you know what 4inches is? we know what 10cm is like. we know what 1cm is like (little finger or so, but everyone can find their own comparison on their body).

bonus: one of my knuckles happens to be exactly 4cm long.