Lean Body Weight

Calculates Lean Body Weight using the Boer formula.

Internal Medicine Internal MedicineEvidence-BasedUpdated 2026-07

Clinical decision-support tool for qualified healthcare professionals. Results are not a diagnosis and should not replace professional clinical judgment.

Clinical Notes

Lean body mass estimates the weight of the body excluding fat mass and is commonly used in clinical nutrition, anesthesia, and drug dosing. The Boer formula uses sex, weight, and height; results are approximate and less reliable at the extremes of body composition, where measured or imaging-based assessment may be preferable.

Calculator Information

Specialty

Internal Medicine

What This Calculator Measures

Estimates lean body weight using the Boer formula, useful for drug dosing, anesthesia, and nutritional assessment.

How to Use

Select the patient's sex.
Enter height (cm) and weight (kg).
Review the estimated lean body weight in kg.
Use it for dosing decisions only where the drug-specific guidance supports lean body weight.

How the Calculation Works

Lean body weight uses the Boer formula: males LBM (kg) = 0.407 x weight + 0.267 x height - 19.2; females LBM (kg) = 0.252 x weight + 0.473 x height - 48.3, with weight in kg and height in cm.

Variables Explained

Sex

Biological sex, which selects the male or female Boer coefficients.

Height

Height in centimeters, multiplied by the sex-specific height coefficient.

Weight

Weight in kilograms, multiplied by the sex-specific weight coefficient.

Interpretation Guide

Lean body weight approximates the weight of body mass excluding fat. Male: 0.407 × weight + 0.267 × height − 19.2. Female: 0.252 × weight + 0.473 × height − 48.3.

Sex-specific interpretation

Clinical Significance

Lean body weight better reflects drug distribution volume than total body weight in some medications, reducing dosing error in patients at the extremes of body size.

When It Is Useful

Drug dosing in medications where lean body weight is the size descriptor (e.g., certain anesthetics and antimicrobials)
Nutritional and metabolic assessment
Anesthesia dosing considerations

When It Is Not Useful

Where the drug label specifies actual or ideal body weight
As a direct measure of body fat or muscle mass
Without confirming the drug-specific dosing guidance

Common Mistakes

Entering height in meters instead of centimeters, which the Boer formula requires.
Dosing a drug with lean body weight when its label specifies actual or ideal body weight.
Reading the result as a direct measurement of body fat or muscle mass.

Limitations

The Boer formula is an estimate validated in adult populations.
May be less accurate at the extremes of body size.
Does not capture hydration status or muscle mass directly.

Worked Example

A 40-year-old man is 180 cm tall and weighs 80 kg.

Inputs:

sex: male

height: 180

weight: 80

Expected Result: LBW = 0.407 × 80 + 0.267 × 180 − 19.2 = 61.4 kg.

Evidence & References

Source:: Body Composition Literature
Reference:: Boer P. Am J Physiol. 1984;247(4):F632-F635.

References

Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans. Am J Physiol. 1984;247(4):F632-F635. (Original Description)

Frequently Asked Questions

When should lean body weight be used for dosing?

Use it when the drug-specific labeling or institutional guidance specifies lean body weight as the dosing size descriptor — it is common in some anesthetic and antimicrobial regimens.

How does lean body weight differ from ideal body weight?

Ideal body weight is a height-based reference, whereas lean body weight is an estimate of the fat-free mass and therefore also incorporates measured weight.

Which Body Weight Calculator Should I Use?

Ideal Body Weight

Height-based dosing reference.

Ignores actual weight.

Adjusted Body Weight

Dosing in overweight and obese adults.

Empirical adjustment factor.

Disclaimer: This calculator is intended for educational and clinical decision support purposes only. Dosing decisions must follow drug-specific labeling and institutional protocols.