Rule of thumb
Suggest a CorrectionMeaning
A practical but approximate guideline based on experience rather than an exact calculation or universal rule.
Origin
The phrase is recorded in Scottish writing before 1658 and in further seventeenth-century examples, where it contrasts rough estimation with measurement by a formal rule or instrument. Thumb was also used as an approximate unit, and craftspeople naturally used their hands for rough measures. The expression does not come from a law permitting a husband to beat his wife with a stick no thicker than his thumb; no such rule gave the phrase its name.
Research Sources
Variants
- As a rule of thumb
- By rule of thumb
Usage Examples
- As a rule of thumb, allow two litres of paint for each small room.
- The estimate is only a rule of thumb; the engineer will calculate the final load.
- Her rule of thumb is to arrive ten minutes before every appointment.