# rule of thumb

Pronunciation: say "rool uhv THUM" US /ˌɹul əv ˈθʌm/, UK /ˌɹuːl əv ˈθʌm/; AUS say "ROOL uhv THUM"

## Noun

1. A general guideline based on experience or common knowledge, used as an approximate measure rather than a strict rule.
   - Simple: A simple guide based on experience that usually works, but is not an exact rule.
   - _Carpenters often rely on a rule of thumb when estimating how much lumber a project needs._
   - _As a rule of thumb, double the recipe if you expect more than eight guests._
2. Arrived at by rough approximation or estimation rather than precise calculation.
   - Simple: Worked out by a rough guess instead of careful measurement.
   - _The engineer offered a rule-of-thumb figure before running the detailed calculations._
   - _Using a rule-of-thumb approach, they sketched the budget in an afternoon._

## Origin

Attested since 1658, the phrase is of uncertain origin but probably comes from using the thumb as a reference for various measurements: for example, the theory that the inch began as the distance between the base of the thumbnail and the first joint, or the practice of wetting the thumb and raising it to judge the wind. The often-repeated claim that it referred to the thickness of a stick a man could use to beat his wife is false and may stem from Del Martin's 1976 book Battered Wives.

Source: DictionaryAI, https://dictionaryai.com/define/rule-of-thumb (written from Wiktionary data, CC BY-SA 4.0: https://creativecommons.org/licenses/by-sa/4.0/).