A pound of feathers or a £ sterling?

The old joke runs “Which weighs more a pound of feathers or a pound of gold?” And the answer is “the feathers”.

The reason is that a pound of gold is a troy pound (~373g), while the pound of feathers is an avoirdupois pound (~453g).

Ever since I found out that there were different pounds I started wondering how much silver (in grams) the British pound was — in the days when it was silver.

The obvious guess is that it was a troy pound, since that is what is currently used for measuring silver.

As with anything to do with the old British currency, the truth is more complicated.

Originally the £ was a tower pound (~350g), first used in 757. Conveniently the tower pound was divided into 240ths called pennyweights, and the British penny is 1/240 of a £.

But the tower pound was abolished in 1527 (in the middle of Henry the VIII’s reign), and the troy pound was used instead. This meant that the pound suddenly changed from ~350g to ~373g. It went up in value by about 1/15th.

I can’t help but wonder what happened to all the old tower coins? Did someone collect up all the old pounds (I suppose a coin that weighed a pound of silver is unlikely), crowns, half crowns, florins, shillings, sixpences, thrupenny bits, and pennies melt them up and strike new coins just a tiny bit bigger? That seems far too difficult a task for the government of those days…

Did people accept the old coins? Was there a complex exchange rate?

English money is an endlessly fascinating topic to me…


I started by looking up hundredweight — one of those odd units (like the pint) which is different in Britain and the US) — and that led me to avoirdupois, which in turn led to pound.

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