Meaning of “rule of thumb” in the English Dictionary

british dictionary

"rule of thumb" in British English

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rule of thumb

C1 a practical and approximate way of doing or measuring something:

A good rule of thumb is that a portion of rice is two handfuls.

(Definition of “rule of thumb” from the Cambridge Advanced Learner’s Dictionary & Thesaurus © Cambridge University Press)

"rule of thumb" in American English

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rule of thumbnoun [ C ]

/ˈrul əv ˈθʌm/ plural rules of thumb

a method of judging a situation or condition that is not exact but is based on experience:

As a rule of thumb, the ice on the lake should be at least two inches thick to support one person.

(Definition of “rule of thumb” from the Cambridge Academic Content Dictionary © Cambridge University Press)