What it means
A handy rough guide, not a law carved in stone. You use it when you want something that’s usually true and good enough for everyday decisions, like timings, measurements, or money. People love repeating a grim origin story about old wife-beating laws, but there’s no solid evidence that’s where the phrase comes from.
Usage examples
"As a rule of thumb, pal, if he says he’ll be ready in ten minutes, add another ten and you’ll save yourself standing around."
"As a rule of thumb, never trust a meeting that runs over an hour, because the actual decisions get made in the corridor on the way out anyway, by the same three people."
"Mum rule of thumb in the kitchen is a handful of salt for the pasta water, and after forty years of cooking nobody has ever complained that her dishes were bland or oversalted."
"Rule of thumb, if the queue outside looks longer than your patience, the food better be unreal or you’re just signing up for disappointment."
"My rule of thumb with flatshares is simple, if nobody buys loo roll till the last square’s doing a farewell dance, move out."
Where it comes from
This one’s old school English, around since the late 1600s. It came from using your thumb as a quick, rough way to measure stuff when you didn’t need laser precision. After that it wandered out of literal measuring and turned into a general handy guideline for everyday life.
