Recipes often measure fresh ginger in "thumbs" or centimetres rather than weight because the ingredient varies so much in shape that a precise measurement can feel unnecessary, according to Guardian food writers.
Felicity Cloake, a food columnist, says there is "no very good answer" to why the imprecise measurements persist. "Maybe it's just convention, because sometimes it feels a bit fussy to give a precise weight for the likes of ginger, onions and other staples."
In many dishes, the exact amount matters less than cooks might think. "If you give a precise weight, people will perhaps think it's very important and worry if they're a few grams out," Cloake says. In curries and similar recipes, small variations rarely affect the outcome.
Fellow columnist Georgina Hayden notes that "cooking should be as instinctive as possible, rather than relying on digital scales." She points out that dishes like curries do not require the precision needed for risotto or baking.
Cloake acknowledges the problem with thumbs as a measuring unit. "If it was a very thick piece, or it wasn't thumb-shaped, I'd cut it so the cumulative flesh of the ginger was roughly the same as the cumulative flesh of a thumb." She adds: "But he's right, we should probably move to grams."