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>USPS charges a flat rate on letters under 370 grams! In the UK the limit for a letter is 100 grams: https://www.royalmail.com/sending/uk/1st-class https://ww

• 2b3a51 10mo ago
  And as that link eventually shows there are limits on the dimensions as well. I sometimes think a simple table might be better than these interactive pages, but I suppose it has to work on a phone. 24 by 16.5 by 0.5 cm for the standard 1st class letter. So you could send an A5 booklet made of less than 20 sheets of A4 (80 g/m^2) paper as a standard letter. If the postage is short, our lovely privatised Post Office holds the letter and makes the recipient pay the excess. Back on thread: Repeatedly fold an A0 sheet of paper in half. How many folds can you do? A ream (500 sheets) of 80 g/m^2 paper is about 2.5cm thick. (good when teaching geometric progressions).