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

A common rule of thumb says to buy builders at one-times book value and sell at two-times.

From Barron's • Jun. 1, 2026

My rule of thumb is to add one cup of cottage cheese for every cup of sauce.

From Salon • May 24, 2026

If you want a good rule of thumb, I say 7% to 10% off of MSRP* is normal, minus any automaker incentives.

From The Wall Street Journal • Mar. 20, 2026

“A very simple rule of thumb for tactical liquidation is when gold and equities crash together, which usually signals margin call / liquidation-esque behavior,” they say.

From MarketWatch • Mar. 20, 2026

“Maybe the flagpole could be a plan B when there isn’t the threat of storms, because avoiding tall metal poles is actually a good rule of thumb when lightning may be in the picture.”

From "A Bird Will Soar" by Alison Green Myers

Related Words

• criterion