RULE OF THUMB

This expression means a practical method of doing or measuring something, usually based on past experience rather than on exact measurement.

Example: As a rule of thumb, you should cook a chicken for 20 minutes for each pound of weight.

The exact origin of the phrase is uncertain. The earliest known citation comes from J Durham’s Heaven upon Earth, 1685: “Many profest Christians are like to foolish builders, who build by guess, and by rule of thumb.”

The term is believed to originate with carpenters who used the length of the tip of their thumbs (ie, inches) rather than rulers for measuring things, cementing its modern use as an imprecise yet reliable and convenient standard. The phrase joins the whole nine yards as one that probably derives from some form of measurement but which is unlikely ever to be definitively pinned down. Reference to spousal abuse

It is often claimed that the term rule of thumb is derived from a law that limited the maximum thickness of a stick with which it was permissible for a man to beat his wife.

According to different sources, English common law before the reign of Charles II permitted a man to give his wife “moderate correction”, but no “rule of thumb” has ever been the law in England.

Belief in the existence of a “rule of thumb” to excuse spousal abuse can be traced as far back as 1782, the year that James Gillray published his satirical cartoon Judge Thumb.

The cartoon lambasts English judge Sir Francis Buller for allegedly ruling that a man may legally beat his wife provided that he used a stick no thicker than his thumb, although there is no other written record of Buller making such a pronouncement.