Lean Body Mass Calculator
This lean body mass calculator estimates everything in your body except fat, from three equations or your own body fat number.
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Field Notes that go deeper
The science behind the lean body mass calculator
Show the formulas, method and sources
Lean body mass is your weight minus your fat. The tool gives it two ways. If you enter a body fat percentage, it subtracts the fat share. Otherwise it applies three equations that use height, weight and sex.
Formulas
From body fat
Lean mass (kg) = weight (kg) x (1 - body fat % / 100)
Boer
Men: LBM = 0.407 x weight (kg) + 0.267 x height (cm) - 19.2Women: LBM = 0.252 x weight (kg) + 0.473 x height (cm) - 48.3
Hume
Men: LBM = 0.3281 x weight (kg) + 0.33929 x height (cm) - 29.53Women: LBM = 0.29569 x weight (kg) + 0.41813 x height (cm) - 43.29
Janmahasatian
Men: FFM = 9270 x weight (kg) / (6680 + 216 x BMI)Women: FFM = 9270 x weight (kg) / (8780 + 244 x BMI)
How it works, step by step
- First, the calculator converts your height and weight to centimeters and kilograms.
- Then, if you entered a body fat percentage, it subtracts the fat share to find lean mass.
- Next, it also applies all three equations for your sex.
- Finally, it shows the lowest and highest equation results as a range, or your body fat result as the headline.
Worked example
For a man who is 180 cm tall and weighs 80 kg, Boer gives 61.4 kg, Hume 57.8 kg and Janmahasatian 61.7 kg, so the result reads 58 to 62 kg. With 20% body fat instead, his lean mass is 80 x 0.8 = 64 kg.
Accuracy and limits
Puri and Blake compared ten equations with DXA scans in 747 men and 811 women aged 60 to 65. Even the best equations had 95% limits of agreement about 11 to 13 kg wide, so one estimate can sit far from a scan.
The three equations also differ from each other by a few kilograms for the same person. That spread shows that none of them can see how much of you is muscle.
Lean mass from a body fat percentage is only as good as the percentage, because the arithmetic simply removes the fat share.
- The comparison study covered adults aged 60 to 65, so results for younger people may differ.
- Lean mass includes muscle, bone, organs and water, so it moves with hydration as well as training.
- Use the range as a rough guide and compare it with a scan result if you have one.
Sources
- Puri T, Blake GM. Comparison of ten predictive equations for estimating lean body mass with dual-energy X-ray absorptiometry in older patients. Br J Radiol. 2022;95(1133):20210378. Used for: The Boer, Hume and Janmahasatian equations as printed, and how far equations sat from DXA.
Sources and math last reviewed: .
Questions people ask
What is lean body mass?
Lean body mass is everything in your body except fat: muscle, bone, organs and water. People also call it fat-free mass and use the two terms almost interchangeably.
What is the difference between lean mass and muscle mass?
Lean mass includes muscle plus bone, organs and water. Because muscle is only one part of it, a change in lean mass can come from water as well as muscle.
Which equation should I trust?
In the comparison study of adults aged 60 to 65, the Janmahasatian and Gallagher equations did best. The tool uses Janmahasatian, Boer and Hume, and it shows all three so you can see the spread.
How do I use my lean mass?
Lean mass feeds other estimates. The Katch-McArdle calculator turns it into resting calories, and the FFMI calculator compares it with your height.
Why does my result differ from my scan?
The equations use height, weight and sex alone, so they cannot see your actual body composition. When the numbers disagree, trust the scan and treat the equations as a rough check.
These calculators give general estimates for adults and are not medical advice. For decisions about your own health, talk with a doctor or a registered dietitian. How we write and check things