Weights On Coins

The official tolerances for coinage weights in Australia are surprisingly lax. Here are the official specifications for Australian coinage, as laid down by the law. The column labelled "Remedy in respect of weight" is the legally acceptable tolerance. Scroll down to 5 cent coins and we see the official tolerance for the circulating ("copper and nickel") five cent coin is plus or minus 0.13 grams, giving a range of 2.70 to 2.96 grams. Since coins only lose weight rather than gain weight during circulation, if mints are going to be in error, they choose to err on the high side, allowing worn coins to remain "legal" for longer.

In practice, the Mint usually manages to get better than that, partly out of professional pride at having high-precision, high-accuracy tolerances, partly because any extra weight of metal given away for free is done so at the Mint's expense, since the mint purchases the blanks by weight (they no longer make their own blanks). But it is not obliged by law to be that precise.