Lean Mass Calculator

Lean body mass (LBM) is your total body weight minus your fat. It includes muscle, bone, organs, and body water. It’s the ultimate baseline for setting your protein targets and figuring out if that 2kg you just lost was actually fat or just water.

If you know your body fat percentage, lean body mass = weight × (1 − body fat % ÷ 100). For example, 80 kg at 20% body fat gives 64 kg of lean mass. If you don't know your body fat, estimate it from height, weight, and sex using the Boer (1984) formula: LBM = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2 for men, and LBM = 0.252 × weight + 0.473 × height − 48.3 for women. This calculator runs both methods for you.

No. Skeletal muscle is just one piece of the puzzle. LBM also counts your bones, organs, and water. This means your lean mass will always be a bigger number than your pure muscle mass.

The direct method (using a real body fat measurement) is undeniably the most accurate. If you don't have that, the Boer (1984) formula is the most reliable estimate for adults. Be careful with James—it notoriously underestimates lean mass in people carrying extra weight.

DEXA scans are the gold standard. Skinfold calipers come next if done by a pro. Smart scales (BIA) are convenient but highly sensitive to whether you just drank a glass of water or ate a meal. A DEXA scan is worth the $50-$100 reality check.

Stop guessing. This calculator sets a baseline target of 2.2 g of protein per kg of lean body mass. If you are actively dieting, research proves you need 2.3–3.1 g/kg LBM to stop your body from burning your hard-earned muscle for fuel.

Absolutely. Tracking your lean mass alongside your scale weight is the only real way to know if you are losing fat or just starving your muscles. Just make sure to use the same measurement method every time to keep it consistent.

Here is the reality: inactive adults lose 3–8% of their muscle mass every decade after age 30. But you have complete control over this. You can stop this decline entirely by lifting heavy things and hitting your protein targets.

It depends on sex and context. For men, 75% lean mass means 25% body fat — on the higher end but within a normal range. For women, 75% lean mass (25% body fat) is solidly healthy. Athletes typically carry 80–95% lean mass (men) or 75–85% (women). Use this calculator to get your exact percentage and compare it against clinical benchmarks.

200 lb (about 91 kg) of lean mass is very high and typical only of large or highly muscular men — for example a 6'2", 240 lb man at 17% body fat. Most men carry 130–180 lb of lean mass and most women 90–130 lb, scaling with height and weight. It isn't a target to chase; what matters is your lean mass relative to your frame and whether it holds steady or rises over time.

Healthy lean mass generally ranges from 60–90% of total body weight, varying by sex, age, and fitness level. Men typically carry 75–90% lean mass, while women carry 65–85%. Rather than chasing a single number, track your lean mass over time — a rising trend means you are gaining or preserving muscle while losing fat.

Because your scale weight alone tells you almost nothing useful. Knowing your lean mass lets you set accurate protein targets, detect whether weight loss is coming from fat or muscle, calculate a meaningful metabolic rate, and track real progress in a way that BMI and body weight simply cannot.