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

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Example Sentences

See Examples For:

rule of thumb

A good rule of thumb is that the amount of protein you have for each meal should fit into the palm of your hand.

From BBC ● Oct. 15, 2026

Here’s a simple rule of thumb for assessing all these claims: None of them is true.

From Los Angeles Times ● Oct. 6, 2026

Thom Bettridge, an editor and writer in New York, has a rule of thumb: he only buys gifts that are smaller than a breadbox, to minimize the space that they take up in hosts’ homes.

From The Wall Street Journal ● Sep. 14, 2026

This should amount to significantly more than the 15% to 20% rule of thumb generally used for retirement savings.

From MarketWatch ● Sep. 2, 2026

Restricting the computers from joining the editorial meetings wasn’t a rule: it was a rule of thumb.

From "Hidden Figures" by Margot Lee Shetterly

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