What does “rule of thumb” mean?

Uncover the fascinating history and versatile definitions behind the popular phrase 'rule of thumb', a practical guide for decision-making and measurement based on practical experience and general principles.

Definition and Origin

The idiom “rule of thumb” has multiple definitions.

It can refer to an approximate method of doing something based on practical experience rather than theory, a general principle that provides a rough guide for decision-making, or a method of measurement based on the width of one’s thumb.

Here are three example sentences that use the idiom:

  1. She uses the rule of thumb to estimate how much time it will take to complete a project.
  2. His rule of thumb is to always check the weather before planning outdoor activities.
  3. The rule of thumb for cooking pasta is to use one gallon of water per pound of pasta.

Here are three synonyms of the idiom:

  • General principle
  • Rough guide
  • Approximation

Etymology and Early Usage

The origin of the idiom “rule of thumb” is uncertain, but it is believed to have originated in the 17th century.

One theory suggests that it comes from the practice of using the thumb as a rough measurement for various items such as spices or cloth.

The Oxford English Dictionary (OED) cites the earliest known usage of the phrase in 1692, where it was used in a figurative sense to mean “a general principle.”

Is “Walking on Eggshells” a Similar Idiomatic Phrase to “Rule of Thumb”?

The meaning of walking on eggshells is similar to the rule of thumb in that both phrases describe a cautious approach to a situation.

While “rule of thumb” suggests a general principle, “walking on eggshells” implies a delicate and tense environment where one must be careful not to upset anyone.

Historical Context

The idiom “rule of thumb” has been associated with English common law, where it was believed that a man could legally beat his wife with a stick no thicker than his thumb.

However, this belief has been debunked as a myth.

The idiom has also been linked to various trades where quantities were measured by comparison to the width or length of a thumb.

In modern times, the idiom “rule of thumb” is often used to describe a general principle or a rough guide for decision-making.

It is commonly used in everyday conversation and is included in many English dictionaries, including the Merriam-Webster Dictionary.