BMI-based body-fat estimate and mass breakdown
The percentage is a regression estimate, not a body-composition measurement. Fat mass is your entered weight multiplied by the estimated percentage; non-fat mass is the remainder. Weight outputs use your selected unit.
To compare a different height-and-weight model or use a known fat percentage, open the Lean Body Mass Calculator .
The formula
The Deurenberg adult equation encodes male as 1 and female as 0. It uses kilograms and meters internally, with exact conversions of 0.45359237 kg per pound and 2.54 cm per inch. Fat mass and non-fat mass use the unrounded percentage; only the displayed outputs are rounded.
A BMI-based estimate for an adult male
At age 30, 170 cm, and 70 kg, BMI is 24.22145. Male coefficients give 1.20 × 24.22145 + 0.23 × 30 − 10.8 − 5.4 = 19.76574%, displayed as 19.77%. Estimated fat mass is 13.84 kg, leaving 56.16 kg of non-fat mass.
How to use this calculator
- Select the equation’s sex coefficients and enter adult age.
- Enter height and body weight in the selected units.
- Calculate and read the BMI-based percentage together with the method limits.
What this method actually estimates
The model relates height and weight to body fat while accounting for age and the sex-specific coefficient. Two people with the same BMI can receive different model results when those inputs differ. The equation does not examine muscle distribution, skinfolds, waist measurements, or an image of body composition. The mass breakdown follows from the estimated percentage; it is not a second independent measurement.
Keep repeated comparisons consistent
When comparing entries over time, keep the units, formula, and measurement procedure consistent. A change in scale weight affects both BMI and the estimated fraction. The model cannot say whether that change came from fat, muscle, water, or another component. Small displayed decimal differences may therefore exceed the information supplied by the inputs. Two decimal places help check arithmetic but do not imply that body fat is known to that precision.
Read the supported range before interpreting a result
This implementation is restricted to adult ages 18–83 and BMI 13.9–40.9, avoiding extrapolation beyond the broad ranges described in the original study. These limits are model boundaries, not health classifications. The equation is not designed for children or pregnancy and can differ from an individual measurement, especially with unusual muscularity or body composition. It provides no body-fat category, target percentage, diet plan, or medical interpretation.
Assumptions & limitations
What this calculation assumes
- Uses the adult Deurenberg regression and its male/female coefficient convention.
What to keep in mind
- Supports ages 18–83 and BMI 13.9–40.9; other values are rejected rather than extrapolated.
- No tape-measure, skinfold, impedance, or DXA inputs; estimated non-fat mass is not skeletal muscle mass.
Common questions
Is this the Navy circumference formula?
No. This page uses the adult BMI, age, and sex equation by Deurenberg. It does not use neck, waist, or hip measurements.
Can two adults with the same BMI have different estimates?
Yes. The equation includes age and sex-specific coefficients. Their actual body composition can also differ from either estimate.
Why does the calculator reject some height and weight combinations?
The resulting BMI falls outside the supported model range. Check the chosen units and measurements; the calculator does not force an out-of-range result into a plausible percentage.