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.

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

#ballpark figure#off the top of my head#down to earth#across the board

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