rule of thumb
Meaning
A practical, rough guideline based on experience rather than precise rules or research.
Origin
Recorded from the late 1600s; it originally referred to a rough method of measurement using the width/length of a thumb. A popular claim links it to an old legal right to beat one’s wife with a thumb-sized stick, but historians find no solid evidence for that as the origin.
Notes
Signals a handy guideline, not a precise rule. Common in conversation and business; often used to soften claims or indicate an estimate.
Examples
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As a rule of thumb, save at least 10% of your income each month.
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A good rule of thumb is to cook fish for about 10 minutes per inch of thickness.
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When packing for a trip, my rule of thumb is to bring one versatile jacket and layer the rest.
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There’s no exact formula, but a rule of thumb is to speak for about two minutes per slide.
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As a rule of thumb, if the deal sounds too good to be true, it probably is.
Grammar & Usage Notes
Usually used with the article: “a rule of thumb.” Common patterns: “As a rule of thumb, …” / “A good rule of thumb is to …” It’s fairly fixed; plural “rules of thumb” is possible.
Synonyms
- general guideline
- rough guideline
- heuristic
- ballpark estimate
- rule of thumb
Antonyms
- exact rule
- hard-and-fast rule
- precise guideline