rule of thumb

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rule of thumb

An approximation; a suggested method or guideline. A good rule of thumb is to plant your seedlings around the end of May.
See also: of, rule, thumb

rule of thumb

a general principle developed through experiential rather than scientific means. As a rule of thumb, I move my houseplants outside in May. Going by a rule of thumb, we stop for gas every 200 miles when we are traveling.
See also: of, rule, thumb

rule of thumb

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]
See also: of, rule, thumb