The Physical activity level is a way to express a person's daily physical activity in a number. This number is defined as a multiple of the Basal metabolic rate, which is the amount of energy consumed while inactive (for example, while the person sleeps). The Physical activity level decreases with age. It can be used to compute the amount of energy one needs to eat in combination with the Basal metabolic rate computed from the Harris-Benedict equations, for example.

The following table shows indicative numbers for the Physical activity level for several lifestyles:

Sedentary	1.2
Light activity	1.5
Moderate activity: standing jobs with some walks	1.8
Very active: walking job	2.0
Extremely active: active job with lots of sport	2.2+

The Physical activity level can also be estimated based on a list of the (physical) activities people perform from day to day. Each activity is connected to a number, the Physical activity ratio. The Physical activity level is then the time-weighted average of the Physical activity ratios. The following calculator contains a form that computes the Physical activity level based on a list of daily activities with their Physical activity ratios.