- Estimated lean mass
- 56 kg
- Estimated fat mass
- 14 kg
How it works
Input uncertainty becomes mass uncertainty
At 70 kg, changing entered body fat from 20% to 25% changes calculated lean mass from 56 to 52.5 kg. That 3.5 kg difference can arise entirely from the percentage assumption, without any measured tissue change.
Understanding lean body mass estimates
Lean body mass is estimated here from either an entered body-fat percentage or a selected reference equation. These approaches can produce different values because they depend on different assumptions. Use the age-appropriate mode and check height and weight units. The output is an estimate of mass outside the modeled fat component, not a direct measurement of skeletal muscle alone.
From body fat: formula and assumptions
Lean mass = weight × (1 − body fat / 100).
The estimate depends directly on the accuracy of your body-fat percentage.
Boer equation: formula and assumptions
Male: 0.407w + 0.267h − 19.2. Female: 0.252w + 0.473h − 48.3.
The Boer regression uses kilograms and centimeters and is an estimate for adults.
Pediatric Peters estimate: formula and assumptions
Estimated lean mass=3.8×0.0215×weight(kg)^0.6469×height(cm)^0.7236.
A pediatric body-composition estimate derived from extracellular volume. This educational calculation must not be used to determine medication doses. Check interpretation with a clinician.
James & Hume comparison: formula and assumptions
James uses a sex-specific quadratic of weight/height; Hume uses sex-specific linear height and weight terms.
Show the selected historical estimate with its population limits. James is unavailable beyond its decreasing-mass turning point. Hume’s original guidance is for males over 16 and females over 30.
Worked example
Using the From body fat example:
- Measurement system
- Metric (kg, cm)
- Weight (kg)
- 70
- Body fat (%)
- 20
Lean mass = weight × (1 − body fat / 100).
Example result
Estimated lean mass: 56 kg
Estimated fat mass: 14 kg
These are illustrative inputs. Change the values to explore a different scenario.
Formula references
- Boer: estimated lean body mass (opens in a new tab)
- Peters et al.: estimation of lean body mass in children (opens in a new tab)
- Pediatric Pharmacokinetics study: published Peters equations 8 and 9 (opens in a new tab)
- Puri and Blake (2022), comparison of ten LBM equations, Table 2 (opens in a new tab)
- Hume (1966): Prediction of lean body mass from height and weight (opens in a new tab)
References explain the underlying methods; they do not imply endorsement or individual professional review of Finflo.
Common questions
Why can the body-fat and equation methods disagree?
One subtracts an entered fat fraction from body weight; regression equations infer lean mass from other measurements and population relationships.
Is the pediatric estimate suitable for calculating a medication dose?
No. The Peters mode is an educational body-composition estimate. Clinical interpretation and medication dosing require a clinician.
Prepared by Finflo. See our methodology and editorial policy. Read the relevant professional-advice limitations.