Lean Body Mass Calculator - Fat Mass & Lean Mass

Formula	weight × (1 − body fat % ÷ 100)
Includes	Muscle, bone, organs, water
Output	Lean mass + fat mass
Use	Track muscle retention

What is Lean Body Mass Calculator?

Lean body mass is everything in your body that is not fat: muscle, bone, organs and water. It is the number athletes watch during a cut, because the goal is to lose fat while holding on to muscle. The calculation is simple once you know your body fat percentage — multiply your weight by one minus body fat as a decimal. If you do not have a body fat number, the calculator estimates it with the Navy tape method from a few circumference measurements. Tracking lean mass month to month tells you whether your training and protein intake are doing their job, in a way the scale alone never can.

Common Uses for Lean Body Mass Calculator

See how much of your weight is muscle and other lean tissue
Check whether a diet is costing you muscle
Set protein targets based on lean mass rather than total weight
Track body composition across a training block

Frequently Asked Questions

Is lean body mass the same as muscle?

Not quite. Lean body mass includes muscle but also bone, organs, connective tissue and body water. Muscle is typically about half of lean mass in a healthy adult.

How do I increase lean body mass?

Resistance training with progressive overload, adequate protein (roughly 1.6–2.2 g/kg), a small calorie surplus for muscle gain, and enough sleep. Lean mass also falls naturally with age without training.

Does lean body mass include water?

Yes. Body water is a large part of lean mass, which is why hydration and measurement timing can shift a lean-mass estimate slightly between readings.