And human weight in stones. Been living here for more than 10 years and still can't remember how much is a stone.
They're nice and vague enough that it's like .. if I go from 10 stone to 11 stone, I need to care. If I go from 10 to 10.1 I don't need to care. I don't convert them to pounds or kilos because I don't want to know the answer, it just adds anxiety that I don't need.
The funny thing is I'm otherwise metric-all-the-things. But for body weight, the lack of precision lets me focus on the trends instead of worrying about the details.
From my d&d days (when we mix and matched Italian and English material) I remember that 2.5lbs is about 1kg, but that's a very rough approximation. Similarly I remember that 10ft is ~3m.