Since the paper weight being measured in grams per square metre, and: - The A0 sheet is a square metre - A1 is half that, A2 half again etc. - It's simple to

Since the paper weight being measured in grams per square metre, and: - The A0 sheet is a square metre - A1 is half that, A2 half again etc. - It's simple to calculate the weight of any particular A-series sheet. This is (nowadays only rarely) useful when determining the postage. If I have 6 A4 pages of typical 80g/m² office paper to post, the weight is 6 × (80 / 2 / 2 / 2 / 2) = 30g. Until recently, the cheapest national postal rate was for up to 50g, so this was a relevant calculation for the once-in-five-years I sent a multipage letter.