Complete guide
Body fat calculator using a published adult prediction equation
Enter adult age, sex, height and weight. Calculator24 calculates BMI, estimates body-fat percentage with the published adult equation and separates estimated fat mass from fat-free mass in a visual chart.
How this body-fat estimate works
The Deurenberg equation predicts body-fat percentage from BMI, age and sex. It was developed from densitometry data and offers a low-cost population estimate without tape measurements or devices.
Adult body-fat formula
The equation codes male as 1 and female as 0. It was reported separately from the paper's child equation; this calculator is limited to adults.
BF%=1.20×BMI+0.23×age−10.8×sex−5.4BMI=kg/m²Worked example
At 68 kg and 165 cm, BMI is about 24.98. For a 35-year-old woman: 1.20×24.98 + 0.23×35 − 5.4 ≈ 32.6%.
Fat mass and fat-free mass
Estimated fat mass equals body weight multiplied by the predicted percentage. Fat-free mass is the remainder. Both inherit the uncertainty of the percentage estimate.
fat mass=weight×BF%fat-free mass=weight−fat massExpected prediction error
The original adult model reported R² 0.79 and a standard error of estimate of 4.1 percentage points. A displayed 30% should therefore not be read as laboratory-level precision.
Population and method limits
Prediction bias can vary with age, ancestry, training status and body composition. DXA, densitometry, bioimpedance and skinfold methods also use different assumptions. Use consistent methods for trend comparisons.
Ways to assess body composition
| Method | What it uses |
|---|---|
| BMI-age-sex equation | Height, weight, age, sex |
| Circumference | Tape measurements |
| Bioimpedance | Electrical impedance model |
| DXA | Low-dose X-ray attenuation |
| Densitometry | Measured body density |
Frequently asked questions
Does this directly measure body fat?
No. It predicts body fat from BMI, age and sex.
How accurate is the equation?
The original adult study reported a standard error near 4.1 percentage points.
Why does age affect the estimate?
Age was an independent term in the published statistical model.
Can athletes use it?
They can view it, but unusual muscularity can make BMI-based predictions less representative.
Can children use this equation?
No. The source paper used a different child equation and this tool is adult-only.
What to keep in mind
This low-cost population screening estimate is not a body-composition measurement. The original adult equation reported a standard error around 4.1 percentage points and may have population-specific bias.
Results display up to 8 decimal places; exported numbers preserve calculation precision. This is a calculation summary, not an official certificate.