Explain it like I'm 12
Lean Body Mass Calculator converts body weight and body-fat percentage into lean mass, fat mass and a lean-BMI cross-check.
Lean Body Mass Calculator
Lean Body Mass Calculator estimates lean mass, fat mass and lean BMI from body weight, body-fat percentage and height.
Source references
- U.S. Navy Physical Readiness Program — body composition assessment reference
Formula
Lean body mass = body weight x (1 - body fat percentage). Fat mass = body weight - lean body mass.
Worked example
80 kg at 22% body fat gives 62.4 kg lean mass and 17.6 kg fat mass.
Professional note
Use the same measurement method over time; trend consistency matters more than one decimal place.
Regional and unit assumptions
U.S. Navy circumference method converted from centimetres to inches.
Assumptions and limitations
- Body-fat percentage is assumed to be already estimated.
- Hydration and measurement methods affect the result.
- Not a medical diagnostic tool.
Methodology & Accuracy
How this calculator is checked
CalculationTime pages are built around visible arithmetic: the formula, assumptions, worked example and practical limitations are shown so the result can be checked rather than simply trusted.
Formula used
Lean body mass = body weight x (1 - body fat percentage). Fat mass = body weight - lean body mass.
Standard or basis
U.S. Navy circumference method converted from centimetres to inches.
Where a calculator follows a named legal, trade or industry standard, that standard is cited visibly. Otherwise the page uses transparent general arithmetic and states its limits.Master's Tip
Use the same measurement method over time; trend consistency matters more than one decimal place.
Related calculators
Questions
Is the Navy method exact?
No. It is a field estimate and can differ from DEXA, hydrostatic weighing or clinical assessment.
Why do measurements matter so much?
Small differences in tape position can change the circumference inputs and therefore the estimate.
Calculation note
Lean mass separates the scale number into tissue categories that can be tracked alongside strength, training and nutrition.
Lean body mass needs assumptions beside the result
The calculator keeps the input values, formula trail and limitation note visible so the result can be checked later instead of treated as a magic number.
The printable record is part of the calculator
A useful result is one that can be compared with a statement, plan, workout log, timetable or worksheet after the page is closed.