Lean Body Mass Calculator (From Body Fat Percentage)

Boer and Hume: lean mass from height and weight alone

Two older formulas estimate lean body mass without a body fat measurement, and both are still used in clinical pharmacology to scale drug doses. Boer (1984) gives, for men, lean mass = 0.407 x weight (kg) + 0.267 x height (cm) minus 19.2, and for women 0.252 x weight + 0.473 x height minus 48.3. Hume (1966) gives, for men, 0.32810 x weight + 0.33929 x height minus 29.5336, and for women 0.29569 x weight + 0.41813 x height minus 43.2933. For an 80 kg, 180 cm man, Boer returns 61.4 kg and Hume 57.8 kg; for a 65 kg, 165 cm woman, Boer returns 46.1 kg and Hume 44.9 kg.

Their limit is the thing they leave out. Because they see only height and weight, they assume an average body composition for that size, so they overstate lean mass in people carrying extra fat and understate it in muscular people. Hume's equation was derived in a small mid-century sample and tends to read low in taller and heavier adults compared with modern DXA scans. Boer's was built to normalize body fluid volumes, not to track training, and is the more common clinical choice today. They are listed here as prose because this page computes lean mass from a measured body fat percentage, which is more accurate whenever you have one.

If you have no body fat estimate, the US Navy circumference method on the body fat calculator (waist, neck and height, plus hip for women) gives one within about 3 to 4 percentage points of underwater weighing for most people, and it takes a tape measure and two minutes.

Why lean mass matters during weight loss, including on GLP-1 medicines

Any weight loss takes some lean mass with it. In the STEP 1 trial of semaglutide (Wilding and colleagues, 2021), the DXA substudy found that roughly 40 percent of the weight lost was lean mass, a proportion similar to diet-induced loss, and the same concern applies to tirzepatide and to any aggressive calorie deficit. Lean mass lost is resting metabolism lost, strength lost and, in older adults, independence lost, and it is slower to regain than fat.

Two things protect it: resistance training two or three times a week, and enough protein. The systematic review by Helms and colleagues (2014) in lean, resistance-trained people under calorie restriction found that 2.3 to 3.1 g of protein per kilogram of fat-free mass per day best preserved lean tissue, scaled upward with leanness and the size of the deficit. Outside a deficit, the meta-analysis by Morton and colleagues (2018) in people doing resistance training found gains in muscle plateaued at about 1.6 g per kilogram of total body weight per day. Clinicians commonly aim between those figures for people on GLP-1 therapies; the right number for you depends on kidney health, age and goal, and is a conversation with your clinician or dietitian.

Tracking lean mass every one to three months, with the same method each time, tells you whether a weight loss program is removing fat or muscle. A scale that shows a falling number and a tape measure that shows a shrinking waist, with lean mass holding steady, is the pattern you want.

Methodology and sources

The calculator computes lean body mass as body weight in kilograms multiplied by one minus the body fat fraction, then applies the Katch-McArdle equation for resting energy expenditure: 370 + 21.6 x lean body mass in kg, published by Katch and McArdle in the third edition of Nutrition, Weight Control, and Exercise (Lea and Febiger, late 1980s). The equation was derived in adults by regressing measured resting metabolism on fat-free mass, which makes it independent of age and sex but entirely dependent on the accuracy of the body fat figure. A body fat estimate from a circumference method or a consumer bioimpedance scale carries an error of 3 to 5 percentage points, which moves the lean mass result by about 2 to 4 kg for an 80 kg adult and the resting energy by 50 to 90 kcal. At very low body fat (under 8 percent in men, 15 percent in women) and at very high body fat the equation is less reliable, and it has not been validated in children.

How this is calculated: a person weighing 80 kg at 20 percent body fat has 80 x (1 minus 0.20) = 64 kg of lean mass, and a resting energy expenditure of 370 + 21.6 x 64 = 1752.4 kcal per day. Lean mass in pounds is the kilogram figure times 2.2046, so 64 kg is 141.1 lb. A weight entered in pounds is converted to kilograms by dividing by 2.2046 before the arithmetic.

The result bands group lean mass into ranges for orientation and give the protein arithmetic for each, using 1.6 g per kilogram of body weight (Morton and colleagues, 2018) and 2.3 to 3.1 g per kilogram of fat-free mass (Helms and colleagues, 2014) as published reference points, not as prescriptions. Lean mass has no healthy range on its own; it is judged against height, sex and age, usually as the fat-free mass index (lean mass divided by height in meters squared), and against change over time measured the same way. The Boer and Hume formulas in the section above are described for comparison and are not computed here.

Medical review: Medical review pending. Last updated October 8, 2026.

References

1. Katch FI, McArdle WD. Nutrition, Weight Control, and Exercise. 3rd ed. Philadelphia: Lea and Febiger.
2. Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans. Am J Physiol. 1984;247(4 Pt 2):F632-F636.
3. Hume R. Prediction of lean body mass from height and weight. J Clin Pathol. 1966;19(4):389-391.
4. Helms ER, Zinn C, Rowlands DS, Brown SR. A systematic review of dietary protein during caloric restriction in resistance trained lean athletes: a case for higher intakes. Int J Sport Nutr Exerc Metab. 2014;24(2):127-138.
5. Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med. 2018;52(6):376-384.