Body Fat Calculator
Estimate body fat percentage from your BMI, age and sex.
How to use this tool
- Enter weight, height, age and sex in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your body fat and the full breakdown beneath it.
Estimate body fat percentage from your BMI, age and sex.
⚠ This tool is for general information and education only and is not medical advice. Consult a qualified healthcare professional before making health decisions.
Formula
Body fat (%) = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4
Where BMI = weight (kg) ÷ height (m)2, and sex = 1 for male, 0 for female.
This is the Deurenberg equation (1991).
How it works
This calculator applies the Deurenberg equation, which uses BMI, age, and sex to estimate body fat percentage without requiring specialised equipment. The sex term (10.8 for males) reflects typical differences in fat-free mass distribution between biological sexes.
The Deurenberg equation carries a reported standard error of around ±3–4 percentage points compared with dual-energy X-ray absorptiometry (DEXA) scans; it is a population-level estimate and should not replace clinical body-composition testing.
Worked example
- Inputs: 70 kg, 175 cm, age 30, male.
- Calculate BMI: 70 ÷ (1.75)² = 70 ÷ 3.0625 = 22.857.
- Apply Deurenberg formula: 1.20 × 22.857 + 0.23 × 30 − 10.8 × 1 − 5.4.
- Compute: 27.429 + 6.9 − 10.8 − 5.4 = 18.13%.
Body fat = 18.13%
Common mistakes to avoid
- Expecting the same precision as a DEXA scan — the Deurenberg BMI-based formula has a standard error of ~3-4%, so treat results as an estimate range.
- Using body weight in pounds instead of kg when computing the BMI sub-step, inflating BMI and therefore overstating body fat percentage.
- Comparing results to athlete body-fat standards — the Deurenberg equation was validated on general populations and overestimates fat in highly muscular individuals.
Key terms
- Body fat percentage
- The proportion of total body mass that is composed of adipose (fat) tissue, expressed as a percentage.
- Deurenberg equation
- A 1991 regression formula that estimates body fat percentage from BMI, age, and sex, validated against underwater weighing data.
- Adipose tissue
- Connective tissue that stores energy in the form of fat; distinguished from essential fat needed for bodily functions and storage fat accumulated in adipose tissue.
- DEXA scan
- Dual-energy X-ray absorptiometry; a gold-standard clinical method for measuring body composition including fat mass, lean mass, and bone density.
- Fat-free mass
- The portion of body weight excluding fat, comprising muscle, bone, water, and organ tissue.
Frequently asked questions
- What is a healthy body fat percentage for men and women?
- General health ranges: men 10-20%, women 18-28%. Athletes often fall below these ranges while remaining healthy.
- Why does this calculator use BMI instead of measurements?
- The Deurenberg equation derives body fat from BMI, age, and sex — inputs easy to obtain without calipers or a tape measure. More precise methods (DEXA, hydrostatic weighing) require equipment.
- Can this formula be used for children?
- No — the Deurenberg (1991) equation was validated for adults. A modified version exists for children with different constants.