Basal metabolic rate (BMR), and the closely related resting metabolic rate (RMR), is the rate of energy expenditure by humans and other animals at rest, and is measured in kJ per hour per kg body mass. Rest is defined as existing in a neutrally temperate environment while in the post-absorptive state. In plants, different considerations apply.

The release, and using, of energy in this state is sufficient only for the functioning of the vital organs: the heart, lungs, nervous system, kidneys, liver, intestine, sex organs, muscles, brain and skin.