Quick answer: For a man of 70 kg and 170 cm, the Boer formula gives 0.407 × 70 + 0.267 × 170 − 19.2 = 54.7 kg of lean mass, about 78% of body weight.
How it's calculated
Boer (1984): men 0.407W + 0.267H − 19.2; women 0.252W + 0.473H − 48.3. James (1976): men 1.1W − 128(W/H)²; women 1.07W − 148(W/H)². Hume (1966): men 0.32810W + 0.33929H − 29.5336; women 0.29569W + 0.41813H − 43.2933. W is weight in kg, H height in cm.
These formulas were made for medicine, for example to dose drugs that do not spread into fat. Boer is shown first because it holds up across a wide range of body sizes; the James formula gives falling results at high BMI, so it is hidden from BMI 35.
The formulas only see height and weight, so two people with the same numbers get the same answer even if one is far more muscular. If you know your body fat percentage, lean mass = weight × (1 − body fat %) is more personal; the body fat calculator estimates it from tape measurements.
Worked examples
- Man, 70 kg, 170 cm: Boer 54.7 · James 55.3 · Hume 51.1 kg
- Woman, 60 kg, 165 cm: Boer 44.9 · James 44.6 · Hume 43.4 kg
Frequently asked questions
What is lean body mass?
Your total weight minus your fat mass: muscle, bone, organs, skin and body water.
Is lean body mass the same as muscle mass?
No. Muscle is only part of it, roughly half in most adults; bone, organs and water make up the rest.
Why do the formulas give different answers?
Each was fitted to a different group of people with different methods. Differences of a few kilos are normal.
How do I work out my fat mass?
Subtract lean body mass from your weight. If you weigh 70 kg and your lean mass is 54.7 kg, the rest, about 15.3 kg, is fat.
How can I increase lean mass?
Regular strength training with enough protein is the most effective approach. Progress is slow, so expect changes over months rather than weeks.
Does lean mass fall with age?
Yes. It tends to decline from middle age, faster without exercise. Strength training helps to slow the loss.