Lean Body Mass Calculator
Lean body mass calculator: estimate lean mass with the Boer, James and Hume formulas or your body fat, and see why the formulas miss muscular lifters.
Lean mass flat for months? Find out what is stopping the gain.
If you know it, we add a direct estimate.
| Method | lb | kg | % of weight |
|---|---|---|---|
| Boer (1984) | 135.6 | 61.5 | 75% |
| James (1976) | 138.5 | 62.8 | 77% |
| Hume (1966) | 126.9 | 57.6 | 71% |
These formulas predict lean mass from height and weight only, so they cannot tell a muscular lifter from an untrained person of the same size. Hume's equations, for example, came from 29 men and 27 women measured by total body water.
Sources: Boer 1984 (as given by Caruso et al. 2018); James 1976 (male multiplier 128, DICOM CP-1612); Hume 1966, J Clin Pathol.
Numbers not moving for weeks? Find out why- Updated
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- LiftDecode
This lean body mass calculator estimates everything you carry that is not fat: muscle, bone, organs and water. It gives two kinds of answer. Three clinical formulas (Boer, James and Hume) use only your height, weight and sex; the body-fat method subtracts your measured fat. For a lifter, only the body-fat method can show muscle you have built.
How do you use the lean body mass calculator?
Enter your sex, height and weight, and add a body fat percentage if you have one. You get the three formula estimates side by side and, with body fat, your lean mass from weight × (1 − body fat ÷ 100).
Use the same body fat method every time, at the same time of day. The trend matters more than any single reading.
Which lean body mass formulas does it use?
Three equations from clinical research, built for jobs such as drug dosing rather than tracking muscle (lean body mass):
- Boer (1984): men 0.407W + 0.267H − 19.2; women 0.252W + 0.473H − 48.3 (W in kg, H in cm). It was the better of two formulas for dosing CT contrast in 55 patients with a BMI above 35 (Caruso et al., 2018).
- James (1976): men 1.10W − 128(W/H)²; women 1.07W − 148(W/H)². The male constant is 128; 120 is a common misquote (DICOM CP-1612).
- Hume (1966): built from total body water measured in 29 men and 27 women (Hume, 1966).
How accurate are the formulas for lifters?
Not very. They only know height, weight and sex, so a muscular lifter and an untrained person of the same size get the same answer.
| Person | Boer | James | Hume | Body fat method |
|---|---|---|---|---|
| Man, 180 lb, 5′10″, 15% fat | 61.5 kg | 62.8 kg | 57.6 kg | 69.4 kg |
| Woman, 140 lb, 5′5″, 25% fat | 45.8 kg | 46.1 kg | 44.5 kg | 47.6 kg |
For the lean man the formulas fall 7–12 kg (15–26 lb) short of his measured lean mass. These are calculations from the equations above, not measurements.
What is a normal lean body mass?
For young adults, the median fat-free mass index is 18.9 for men and 15.4 for women (Schutz et al., 2002). That works out to about 60 kg (132 lb) of fat-free mass for a 5′10″ man and 42 kg (93 lb) for a 5′5″ woman. At 5′10″, 160 lb of lean mass is an FFMI of about 23, well above that median; the FFMI calculator adjusts for height.
What if your lean mass isn't going up?
Then you are not building muscle, whatever the scale says. If lean mass stays flat across two or three monthly checks on a bulk, the usual causes are low weekly volume, sets far from failure, eating at maintenance and short sleep. Each extra weekly set adds about 0.37% to muscle growth on average (Schoenfeld et al., 2017). Find out which cause is yours.
FAQ
How do you calculate lean body mass?
With a body fat number, multiply your weight by one minus your body fat fraction: 180 lb at 15% fat is 153 lb of lean mass. Without one, the Boer, James and Hume formulas give a rough estimate from height and weight.
Is 160 lb of lean mass good?
At 5′10″ it is an FFMI of about 23, a very well-trained physique. At 6′2″ the same lean mass is an FFMI of about 20.5.
Does creatine change lean body mass?
It can raise the reading by adding water to muscle, and water counts as lean mass. Read changes over months, not days.
Written and maintained by LiftDecode. Training and nutrition education for healthy adults, not medical advice — if you have a health condition or an injury, talk to a professional who can examine you.