rule of thumb

American  

noun

1. a general or approximate principle, procedure, or rule based on experience or practice, as opposed to a specific, scientific calculation or estimate.

2. a rough, practical method of procedure.

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rule of thumb British  

noun

1. 1. a rough and practical approach, based on experience, rather than a scientific or precise one based on theory

   2. ( as modifier )

      a rule-of-thumb decision

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rule of thumb Cultural  

1. A practical principle that comes from the wisdom of experience and is usually but not always valid: “When playing baseball, a good rule of thumb is to put your best hitter fourth in the batting order.”

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rule of thumb Idioms  

1. A rough and useful principle or method, based on experience rather than precisely accurate measures. For example, His work with the youth group is largely by rule of thumb. This expression alludes to making rough estimates of measurements by using one's thumb. [Second half of 1600s]

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Etymology

Origin of rule of thumb

First recorded in 1685–95

Example Sentences

See Examples For:

rule of thumb

One planner’s rule of thumb is to skip net unrealized appreciation on any shares with a basis above 20 cents on the dollar.

From MarketWatch ● Sep. 10, 2026

A good rule of thumb is that you can make fun of attitudes, behaviors and yes, pants, but not core attributes or misfortunes a person can’t help.

From The Wall Street Journal ● Aug. 30, 2026

The closest thing to a rule of thumb holds that courts should apply the rules of the state that has the most significant relationship to the case.

From Slate ● Aug. 28, 2026

"Always ask, would you put the same thing in an email?" he says, as a rule of thumb.

From BBC ● Aug. 17, 2026

“Over the years military planners have arrived at a rule of thumb which dictates that functional fighting units cannot be substantially larger than 200 men,” Dunbar writes.

From "The Tipping Point" by Malcolm Gladwell

Related Words

• criterion