Body Fat Calculator
Explore a BMI-based Deurenberg body-fat estimate and understand why it is not a measurement.
Your estimate
Enter your values and calculate. Results will appear here.
This rough population-based prediction is useful for understanding how the equation works. It cannot distinguish two people with the same BMI and age but very different muscularity.
How to use this calculator
Enter height, weight, adult age and the formula coefficient. The model uses BMI rather than tape measurements. For repeat comparisons, keep measurement conditions consistent and remember that age and weight changes affect a statistical estimate.
Formula and methodology
Deurenberg adult estimate: body fat % = 1.20 × BMI + 0.23 × age − 10.8 × sex code − 5.4; sex code male = 1, female = 0.
Worked example
For 70 kg, 175 cm, age 30 and the male coefficient, BMI is about 22.857. The equation gives 27.429 + 6.9 − 10.8 − 5.4 = 18.129%, displayed as 18.1%. This is a prediction, not measured fat.
What the result means
This rough population-based prediction is useful for understanding how the equation works. It cannot distinguish two people with the same BMI and age but very different muscularity.
Limitations
The method is not a clinical body-composition test. It can be misleading for muscular individuals and may not transfer equally to all populations. Values outside 5–60% are withheld as outside this tool’s display scope; accepted values are not thereby validated.
Common mistakes
Do not interpret the decimal place as measurement precision. Feeding this estimate into lean body mass carries the same uncertainty forward rather than creating an independent confirmation.
Frequently asked questions
Is this the Navy tape-measure method?
No. This calculator clearly uses the Deurenberg BMI, age and sex equation, without circumference inputs.
Can it measure muscle gain?
No. Changes in this estimate cannot independently identify a change in muscle tissue.