Food that can be eaten with one hand is our rule of thumb.

A good rule of thumb

As a rough rule of thumb, I would say the smaller the pond, the more belligerent the fish.

Or another rule of thumb is to add one car length for every 10 mph you are traveling.

One rule of thumb is for every degree you set back the thermostat, you save 3 percent on your heating bill. That's assuming it's 24 hours per day. If for eight hours of sleep and eight hours of work you set back the thermostat 3 degrees, that's a savings of 6 percent.

In general there's a rule of thumb that one year in the state system is worth two or three in the federal system.