rule of thumb

American  

noun

1. a general or approximate principle, procedure, or rule based on experience or practice, as opposed to a specific, scientific calculation or estimate.

2. a rough, practical method of procedure.

---

rule of thumb British  

noun

1. 1. a rough and practical approach, based on experience, rather than a scientific or precise one based on theory

   2. ( as modifier )

      a rule-of-thumb decision

---

rule of thumb Cultural  

1. A practical principle that comes from the wisdom of experience and is usually but not always valid: “When playing baseball, a good rule of thumb is to put your best hitter fourth in the batting order.”

---

rule of thumb Idioms  

1. A rough and useful principle or method, based on experience rather than precisely accurate measures. For example, His work with the youth group is largely by rule of thumb. This expression alludes to making rough estimates of measurements by using one's thumb. [Second half of 1600s]

---

Etymology

Origin of rule of thumb

First recorded in 1685–95

Example Sentences

But that’s a rule of thumb, not gospel.

From MarketWatch • Jun. 2, 2026

My rule of thumb is to add one cup of cottage cheese for every cup of sauce.

From Salon • May 24, 2026

As a rule of thumb, every $10 rise in oil adds about five cents per pound to polyethylene, according to Morales.

From Barron's • May 12, 2026

If you want a good rule of thumb, I say 7% to 10% off of MSRP* is normal, minus any automaker incentives.

From The Wall Street Journal • Mar. 20, 2026

A useful rule of thumb in this regard is to forget the adults and pay attention to the behavior of the children.

From "Circumference" by Nicholas Nicastro

Related Words

• criterion