RULE OF THUMB

A rule of thumb is a rule or principle based on experience rather than theory or precise calculations.

 Examples:

 “As a rule of thumb, give your plants a little water every other day.”

 “A depreciation of 10% or more in the value of the pound is likely—which, according to a rule of thumb, would increase prices by 2–3%.”

 “As a rule of thumb, thicker fabrics last longer than thinner ones.”


 This idiom was first recorded in 1692 and probably originates from the use of parts of the body as units of measurement. As the first joint of an adult’s thumb is about an inch long, it could be used to make rough measurements [1].


Photo credit: Romain Guilloux (Creative Commons)

[1] Cresswell, Julia. “rule” in The Oxford Dictionary of Word Origins. Oxford University Press, 2009.