The weight that isn’t fat
Muscle, bone, organs and water — your metabolic engine.
Results update as you type 🥑
Why lean body mass matters
Lean body mass (LBM) is everything you carry that is not fat: muscle, bone, organs and water. It drives your metabolic rate, so it largely sets how much you can eat.
Tracking LBM while dieting tells you whether you are losing fat or muscle. Stable LBM with falling weight means the deficit and protein are working.
We use the Boer formula. It is an estimate from height and weight — combine it with a body-fat measurement when you can.
Common questions
What is a good lean body mass?
There is no single target — it scales with frame and training. What matters is keeping it stable or rising while losing fat.
LBM vs fat-free mass?
Nearly the same in practice; fat-free mass excludes essential fat in cells, a tiny difference for most purposes.
How do I increase LBM?
Progressive resistance training plus enough protein (1.6–2.2 g/kg) and adequate calories.
Is my data stored?
No. Everything is calculated in your browser. Nothing is sent to a server or saved.
Sources & references
- Mifflin MD, St Jeor ST, et al. “A new predictive equation for resting energy expenditure in healthy individuals.” Am J Clin Nutr. 1990;51(2):241–247.
- Frankenfield D, Roth-Yousey L, Compher C. “Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults.” J Am Diet Assoc. 2005;105(5):775–789.
This calculator provides estimates for general educational use and is not medical advice. Consult a qualified professional before making significant dietary changes.