mancity2012_eamo
Well-Known Member
A good rule of thumb is to double check any facts you get from this site.In English, the phrase rule of thumb refers to an approximate method for doing something, based on practical experience rather than theory. This usage of the phrase can be traced back to the 17th century and has been associated with various trades where quantities were measured by comparison to the width or length of a thumb.
A modern folk etymology holds that the phrase is derived from the maximum width of a stick allowed for wife-beating under English common law, but no such law ever existed.