There is one cool trick I use with metric paper: since A0 is a square meter, and comprises of 16 A4 sheets, when you see paper with weight per square meter, you

There is one cool trick I use with metric paper: since A0 is a square meter, and comprises of 16 A4 sheets, when you see paper with weight per square meter, you need to divide by 16 to get the weight of a single sheet of paper. In practice regular paper has ~80g/m^2, meaning 5 grams per sheet, meaning a ream of 500 sheets has exactly 2.5 kg.