How this calculator works
Each coin count is multiplied by its nominal Royal Mint mass, then the masses are added. The eight masses in grams are 3.56, 7.12, 3.25, 6.50, 5.00, 8.00, 8.75 and 12.00 in ascending denomination order. Face value uses 100 pence per pound. To recover one count, subtract the mass of the known coins from the measured net mass, divide by the chosen coin mass and round to the nearest whole coin. The residual shows how closely the estimate fits your scale reading. Subtract the container weight first.
Formula
Total mass = sum(count x mass per coin). Face value in pounds = sum(count x denomination in pence) / 100. Missing count estimate = round((measured mass - known mass) / mass of the selected coin).
Worked example
One hundred 1p coins weigh 356 g and are worth GBP 1. Twenty current twelve-sided GBP 1 coins weigh 175 g and have a face value of GBP 20.
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Frequently asked questions
Can weight identify an unknown mixed bag?
No. Different combinations can have the same mass. You must know every count except the one denomination being estimated.
Do older coins use these masses?
Not always. The old round pound, large 5p, large 10p and large 50p coins differ. Use this tool for the current circulating sizes.
Why is my scale reading different?
Wear, dirt, mint tolerance and scale error can affect measured mass. A count recovered from mass is an estimate; check the residual and count manually when accuracy matters.