Idiom
Rule of thumb
A rule of thumb is a rough, practical guideline based on experience rather than exact measurement or science.
How people use it
People use a rule of thumb as a handy shortcut when precision is not needed, for cooking, saving money, travel or home repairs. Typical patterns are "as a rule of thumb" and "a good rule of thumb is to..." A rule of thumb is useful but approximate, and it is not an official rule or a law. It usually works most of the time, with exceptions. The phrase is neutral and fine in both everyday speech and formal writing.
Also said: as a rule of thumb.
Examples
- A good rule of thumb is to save at least three months of expenses.
- As a rule of thumb, leave an hour early when you drive to the airport on holidays.
- My uncle's rule of thumb for steak is to flip it only once.
Where it comes from
No one knows for sure, but the most likely source is the old habit of using the thumb as a rough measuring tool. The width of a thumb is close to an inch, and craftspeople, tailors and brewers judged sizes or temperatures by hand rather than with instruments. The phrase is recorded from the late 1600s. A popular story says an old English law let men beat their wives with a stick no thicker than a thumb, but historians have found no such law, and the phrase was in use long before that claim appeared.
Check yourself
1. What is a rule of thumb?
Answer: A rough guideline from experience. A rule of thumb is practical and approximate, not exact or official.
2. Which statement about the origin of rule of thumb is true?
Answer: No real law about thumbs and punishment has been found. The law story is a myth, and the phrase is older than the claim.
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