How much does a potato weigh?

A potato's weight tracks its size closely, and a medium one — the size most recipes assume — comes in around 170 grams. Small and large run from about 100 to 280 grams.

Potatoes are graded by size before they reach a shop — growers and packers sort them into small, medium and large — but that grade is rarely printed anywhere the shopper can see it, and loose potatoes are sold by weight. So a recipe written for four medium potatoes is describing a size you can pick out by eye, not a category the shop guarantees. Judging by eye gets you within a third either way, which is close enough for a stew and not close enough for baking.