Readers reply: why does tinned food come in a 400g can?

The long-running series in which readers answer other readers’ questions on subjects ranging from trivial flights of fancy to profound scientific and philosophical concepts

Why do so many tinned foods – in Britain, at least – come in cylindrical 400g cans? Who decided that 400g is the perfect amount of beans/tomatoes/custard? Nanci Preston, Solihull

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Presumably, it was originally 1lb (454g), and at the time we switched from imperial to metric units the manufacturers seized the chance to make the tins 12% smaller while keeping the price the same. Shasarak

It looks like a slow transition from imperial to metric measurement with a side of inflation.

When I was a kid, Heinz baked beans were sold in 16oz cans. This dropped over time to 15oz and then to 14oz, but the cans stayed the same size because the equipment to make and fill the cans remained the same.

Sixteen ounces is about 450g, but it doesn't divide well by two. Hence 400g gives us the smaller sizes 200g, 100g, 50g and 25g quite nicely. And if that isn't the reason, maybe it should be. SpiritOf1966

Tins did not become 12% smaller. The only change was from describing the contents in pounds and ounces to metric. The cans retained their physical dimensions. ufs1968

I’m sure it’ll be Brussels’ fault, if you ask the right people. UpVoteThis

It's a subtle way of forcing you to buy more than you really need. A 400g serving is too much for one person, but it's often not enough for two, which means you have to buy two tins, which is more than you really need for two … and so on. mjback

I just weighed an empty tin. It weighs exactly 54g. And 400g + 54g = 454g = 1lb. That means you were easily able to cross-estimate weight/number of cans. I’m off to bed now. So there you are. MackieOvelly

The size doesn't bother me, but why cylindrical? The worst possible shape for storage space. And why do some manufacturers not make them brilliant stackable tins? theseligsussex

Sharp corners in metal are where corrosion gets in, so given tins are primarily to preserve food … Mike345

Doing elementary exercises at differentiation, it's the shape that uses least metal. javathedog

I’m guessing one reason is that tins for larger quantities need the rigidity that a cylindrical shape provides. Eternally_Hopeful

A 400g tin in reality weighs between 385g and 425g. For many commodities, almost half of this can be water, leaving about 240g of contents. So it is unlikely to be because of the weight; more likely the volume. So it probably started life as a number of servings … two? woodworm20

It was decreed by the Catholic church under cannin’ law. GodlessHeathens