Approximately how much of your body weight is muscle?

Approximately 40% of an adult’s body weight is skeletal muscle.

Skeletal muscle is the muscle attached to bones, and it produces voluntary movement, maintains posture, stabilizes joints, and generates heat. It is the largest muscle category in the body and includes familiar groups such as the quadriceps, hamstrings, abdominal muscles, and shoulder muscles.

The figure is an average, not a universal rule. Muscle percentage changes with age, sex, genetics, physical activity, illness, and nutrition. Adult men often have a higher proportion of skeletal muscle than adult women, while children and older adults generally have different body-composition patterns. Athletes may also fall well outside the average.

This estimate can be confused with lean body mass, which includes muscle but also contains water, organs, connective tissue, and bone. It also usually refers to skeletal muscle rather than adding every smooth muscle cell and cardiac muscle in the body. Because “approximately” is built into the question, forty percent is the standard fair answer.