Body fat from BMI calculator
Handy when you cannot take body measurements, since it only needs weight, height, age and sex.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter sex, age, weight and height.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Body fat % = 1.2 × BMI + 0.23 × age − 10.8 × sex − 5.4, with sex 1 for male and 0 for female (Deurenberg 1991).
Example
Inputs: Sex = Male, Age = 30 years, Weight = 70 kg, Height = 175 cm. Result: Estimated body fat: 18.1%; BMI: 22.9; Fat mass: 12.7 kg.
Limits and caveats
- It is a population equation and misreads athletes and very muscular people.
- Made for adults; the error for one person can reach about 4 percentage points.
Questions about this tool
Can it replace the US Navy method?
No. The Navy method uses body measurements and is usually closer; this is a fallback when you have no tape.
Why does age raise the result?
Muscle falls with age while fat rises at the same weight, and the equation reflects that.
Does it work for teenagers?
No. Deurenberg published a separate equation for children; this one is for adults.