# What is my lean body mass?

Estimates lean body mass (everything but fat) from sex, height and weight by the Boer, James and Hume formulas, with the body fat percentage it implies.

- Page: https://www.acalculator.org/health/lean-body-mass-calculator
- JSON spec: https://www.acalculator.org/health/lean-body-mass-calculator.json
- Version: c69efd4c658f

## Default answer

Example with the default inputs (Sex Male, Height 5 ft 10 in, Weight 180 lb): At 5 ft 10 in and 180 lb, your lean body mass is about 135.6 lb by the Boer formula.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| sex | Sex | Sex at birth, which the body formulas use. |
| height | Height | Your height without shoes. |
| weight | Weight | Your body weight. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| boer | Lean body mass (Boer) | Lean body mass by the Boer (1984) formula, in pounds. |
| boerKg | Lean body mass, Boer (kg) | Lean body mass by the Boer formula, in kilograms. |
| fat | Body fat (Boer) | The part of your weight that is not lean mass by Boer: (weight − LBM) ÷ weight. |
| james | Lean body mass (James) | Lean body mass by the James (1976) formula, in pounds; left out past the weight where it peaks. |
| jamesKg | Lean body mass, James (kg) | Lean body mass by the James formula, in kilograms. |
| hume | Lean body mass (Hume) | Lean body mass by the Hume (1966) formula, in pounds. |
| humeKg | Lean body mass, Hume (kg) | Lean body mass by the Hume formula, in kilograms. |
| note | About the James formula | Why the James result is left out, when it is. |

## Method

Boer: men 0.407W + 0.267H − 19.2, women 0.252W + 0.473H − 48.3; James: men 1.1W − 128(W/H)², women 1.07W − 148(W/H)²; Hume: men 0.32810W + 0.33929H − 29.5336, women 0.29569W + 0.41813H − 43.2933 (W in kg, H in cm).

## Assumptions

- The formulas are for adults. They estimate lean mass from height and weight only, not from a body scan.
- Body fat is the weight minus the Boer lean mass, as a percent of the weight.
- Height from 1 to 2.5 m (3 ft 3 in to 8 ft 2 in) and weight from 25 to 350 kg (55 to 772 lb).

## Worked examples

1. sex = male, height = 1.778, weight = 81.646627 gives boerKg = 61.5, boer = 135.6, fat = 24.7%, humeKg = 57.6, hume = 126.9, jamesKg = 62.8, james = 138.5. Source: De Cassai A et al., Regional anesthesia in obese patients, Saudi J Anaesth 2025, lean body mass table: Boer, James and Hume formulas, height in cm, weight in kg (https://europepmc.org/article/PMC/PMC12007849, retrieved 2026-10-02).
2. sex = female, height = 1.65, weight = 60 gives boerKg = 44.9, boer = 98.9, fat = 25.2%, jamesKg = 44.6, humeKg = 43.4. Source: De Cassai A et al., Regional anesthesia in obese patients, Saudi J Anaesth 2025, lean body mass table: Boer, James and Hume formulas, height in cm, weight in kg (https://europepmc.org/article/PMC/PMC12007849, retrieved 2026-10-02); Caruso D et al., Lean Body Weight-Tailored Iodinated Contrast Injection in Obese Patient: Boer versus James Formula, BioMed Res Int 2018 (https://europepmc.org/article/PMC/PMC6110034, retrieved 2026-10-02).
3. sex = male, height = 1.7, weight = 130 gives boerKg = 79.1, humeKg = 70.8, note = The James formula is left out: above 124.2 kg at your height and sex it gives less lean mass for more weight, which is not realistic.. Source: Caruso D et al., Lean Body Weight-Tailored Iodinated Contrast Injection in Obese Patient: Boer versus James Formula, BioMed Res Int 2018 (https://europepmc.org/article/PMC/PMC6110034, retrieved 2026-10-02).

## FAQ

### What is lean body mass?

Everything in your body that is not fat: muscle, bone, organs, skin and water. It is your weight minus your fat mass. Doctors use it to dose some drugs and contrast media, because fat takes up some drugs much less than lean tissue.

### Which lean body mass formula is best?

None is best for everyone. Boer (1984) is the most widely used and is the headline here. James (1976) breaks down at high weights, and Hume (1966) usually gives a little less. A body scan such as DEXA measures lean mass directly.

### Why is the James result missing for me?

The James formula has a (weight ÷ height)² term, so above a certain weight it gives less lean mass the more you weigh, which cannot be right. For a man of 170 cm that peak is 1.1 × 170² ÷ 256 = 124.2 kg. Past the peak the calculator leaves James out.

### How is body fat worked out here?

Body fat % = (weight − lean body mass) ÷ weight × 100, with the Boer lean mass. For a 180 lb man of 5 ft 10 in it is about 24.7%. It is an estimate from height and weight only.

### Can lean body mass change?

Yes. Strength training and enough protein can add muscle, while dieting without exercise can lose some. These formulas cannot see that: they only use height and weight, so two people with the same numbers get the same answer.

### Do the formulas work for children?

No. They were built from adult data. For children, ask a doctor; this page is for adults.

## Sources

- De Cassai A, Zarantonello F, Pistollato E, et al. Regional anesthesia in obese patients: Challenges, considerations, and solutions. Saudi J Anaesth. 2025. Table: Boer, James and Hume lean body mass formulas for men and women (height in cm, weight in kg), retrieved 2026-10-02. https://europepmc.org/article/PMC/PMC12007849
- Caruso D, De Santis D, Rivosecchi F, et al. Lean Body Weight-Tailored Iodinated Contrast Injection in Obese Patient: Boer versus James Formula. BioMed Res Int. 2018;2018:8521893 (Boer and James formulas), retrieved 2026-10-02. https://europepmc.org/article/PMC/PMC6110034
- 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 (abstract), retrieved 2026-10-02. https://europepmc.org/article/MED/6496691