A rule of thumb意思

"A rule of thumb" is an English idiom that refers to a general principle or guideline that is not intended to be strictly accurate but is intended to provide a useful estimate or starting point. It is often based on experience or common sense rather than on scientific or mathematical precision.

For example, "a rule of thumb for determining the right amount of food to serve at a party is to allow for about two slices of pizza per person." This is not a hard and fast rule, but it is a simple and practical guideline that can help you plan for a party.