English expressions: rule of thumb

The expression, "rule of thumb" may have derived from a several independent sources.

One of the ideas comes from ancient punishment methods regarding the thickness of stick used to beat someone. The rod or stick used could not be thicker than the person's thumb.

But now days the expression really just refers to a general guideline for any type of quantity or method of approach to a problem.

thumb

An arbitary width or a rough guide is a rule of thumb.


It may relate to measurements in economics, tailors or situations where things actually involve thumbs, like tasting things using your thumb.

References sources:

http://en.wikipedia.org/wiki/Rule_of_thumb