A broadly accurate practical principle or guide, not intended to be rigorous or applicable in every situation.
Examples:
- A good rule of thumb in the office kitchen is that any mug without a sticker is safe to use.
- As a rule of thumb, allocate 20% of your revenue to marketing in the first year.
Origin: Said to originate in the old English custom of using the width of a thumb as a unit of measurement for trade.
Synonyms: general guideline, rough guide, general principle