phrase🎓 English idiom
a rule of thumb
a rough, practical guideline
What it means
A rough, practical guideline based on experience rather than precise measurement or strict rules. It gives useful general advice that works in most situations but not necessarily every one.
Words like “a rule of thumb” are exactly the kind of vocabulary our English vocabulary size test measures — find out how many English words you know.
Examples
- As a rule of thumb, drink about two litres of water a day.
- A good rule of thumb is to save ten percent of your income.
- Our rule of thumb is to reply to customer emails within 24 hours.
- As a rule of thumb, never go food shopping when you're hungry.
Where it comes from
The phrase, recorded from the late 1600s, probably refers to using the thumb as a rough unit of measurement; a popular claim linking it to wife-beating laws has no historical basis.
Related idioms
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