Lean Body Mass Calculator
Estimate lean body mass from height and weight using the Boer, James and Hume equations, shown side by side.
Result
Enter height and weight to see the result.
https://calcgallery.com/body-composition/lean-body-mass-calculator/
How to use the Lean Body Mass Calculator
- Choose which published equation to apply. The source studies used a female/male binary.
- Enter your height and weight.
- If you have a measured body fat percentage, enter it for the exact split instead of an estimate.
- Compare the three estimates. The gap between them is how uncertain the answer is.
How it is calculated
Lean body mass is total weight minus fat mass. Since fat mass is not directly observable without equipment, three published equations predict lean mass from height, weight and sex instead. All three take weight in kilograms and height in centimetres:
Boer (1984) male LBM = 0.407 × kg + 0.267 × cm − 19.2 female LBM = 0.252 × kg + 0.473 × cm − 48.3James (1976) male LBM = 1.1 × kg − 128 × (kg ÷ cm)² female LBM = 1.07 × kg − 148 × (kg ÷ cm)²Hume (1966) male LBM = 0.32810 × kg + 0.33929 × cm − 29.5336 female LBM = 0.29569 × kg + 0.41813 × cm − 43.2933The James equation is the odd one out. Rather than a straight line in height and weight, it subtracts a correction that grows with the square of weight over height, which makes it bend away from the other two at heavier weights. That is also where its unit trap lives: the ratio is kilograms per centimetre, and using metres inflates the correction ten-thousandfold.
The measured route is better whenever you have it. If you know your body fat percentage from a DEXA scan, calipers or a circumference estimate, then lean mass is simply weight × (1 − body fat). That is arithmetic on a measurement rather than a prediction from a population, so this calculator labels it separately and does not mix it in with the three estimates.
What these equations cannot do. They know only your height, your weight and which equation you asked for. Two people of identical height and weight get identical answers regardless of how differently they are built, which is precisely the situation where lean mass is the interesting number. Nor is any of them validated for children, for pregnancy, or at the extremes of body size where they were never fitted.
Practical tips
Use the spread, not the single figure. Three equations disagreeing by several kilograms is the honest answer. If you need one number, pick one equation and stay with it, so that the change you track over months is not contaminated by switching formulas.
Lean mass moves slowly; scale weight does not. Day-to-day swings of a kilogram or two are water, glycogen and gut contents. Meaningful changes in lean tissue take weeks to months and are easily hidden under that noise.
This is the input the Katch-McArdle equation wants. Of the common resting-energy equations, only Katch-McArdle uses body composition rather than height, weight and age. If you have a real lean mass figure, that equation is the one it improves.
A measured body fat percentage beats all three predictions. Even a tape-measure estimate anchors the answer to something about your actual body. The three regressions have no information about you beyond your dimensions.
Do not compare figures produced by different methods. A lean mass from DEXA, one from a smart scale and one from a regression are three different quantities estimated three different ways. Comparing them tells you about the methods, not about you.
With your numbers
- Three published equations estimate James 101.5 lb, Hume 98.1 lb and Boer 101 lb
Quick reference
Three published equations that disagree. The spread between them is the honest measure of how precise this estimate is.
| Example | Lean body mass, Boer |
|---|---|
| Male, 5 ft 8 in, 160 lb | 124.5 lb |
| Male, 5 ft 10 in, 180 lb | 135.6 lb |
| Male, 6 ft 0 in, 200 lb | 146.7 lb |
| Female, 5 ft 4 in, 130 lb | 95.8 lb |
| Female, 5 ft 6 in, 150 lb | 106.1 lb |
| Male, 180 cm, 80 kg | 61.4 kg |
| Female, 165 cm, 63.5 kg | 45.7 kg |
| Female, 170 cm, 70 kg, 28% measured | 49.8 kg |
Common questions about the Lean Body Mass Calculator
- Is lean body mass the same as muscle mass?
- No, and the difference is large. Lean body mass is everything that is not fat: muscle, bone, organs, connective tissue and the water in all of them. Skeletal muscle is typically somewhere around half of it in an adult. A change in lean mass on a scale over a few days is almost always water, not muscle, because muscle does not appear or disappear at that speed.
- Which of the three formulas should I use?
- There is no basis on this page for preferring one. Boer was derived on a general adult population and is the most widely cited of the three, which is why it is shown first, but that is convention rather than evidence of superiority. All three were fitted on different groups decades apart, which is exactly why they disagree. If you use one, use the same one every time so the comparison over months is meaningful.
- Why does the answer differ from my smart scale?
- A smart scale estimates body fat by bioelectrical impedance and derives lean mass from that, so it is measuring a different physical property by a different route. Impedance readings also move with hydration, recent food, recent exercise and even foot temperature. Neither number is a direct observation of your tissue.
- What is lean body mass used for?
- Two things mainly. Some drug doses are calculated against lean mass rather than total weight, which is what the Boer and James equations were originally published for. And the Katch-McArdle basal metabolic rate equation takes lean mass as its only input, which makes it the one resting-energy equation that responds to body composition rather than just size.
- Why do the three answers disagree by several kilograms?
- Because each is a regression fitted to a different sample of people, using a different reference method, in a different decade. None of them measures your body; each predicts a population average for someone of your height, weight and sex. The spread between them is a fair picture of how much confidence a prediction of this kind deserves.