Health & fitness
Estimate body fat percentage from BMI, age, and sex.
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Body fat percentage calculator guide
This calculator estimates body fat percentage from body mass index, age, and sex using the Deurenberg equation, published in 1991 from a Dutch study of more than 1,200 adults who had body fat measured by densitometry. It first computes BMI from weight in kilograms and height in metres, then applies the regression: 1.2 × BMI + 0.23 × age − 10.8 × sex − 5.4, where sex is 1 for males and 0 for females. Because it needs only a scale and a tape measure, it is a quick screening figure for tracking a trend or for a first look before a more precise method. It is not a measurement of fat: BMI cannot distinguish muscle from fat, so a muscular person will be overestimated and someone with low muscle mass underestimated, and the equation’s standard error is around 4 percentage points. Skinfold calipers, bioimpedance scales, air-displacement plethysmography, and DXA scans measure composition directly. Treat the result as a screening estimate rather than a diagnosis, and discuss body-composition concerns with a clinician.
BMI = weight (kg) ÷ (height (cm) ÷ 100)². Deurenberg body fat (%) = 1.2 × BMI + 0.23 × age (years) − 10.8 × sex − 5.4, where sex = 1 for male and 0 for female. Displayed to one decimal place.
Worked example with the default inputs: a 30-year-old male weighing 70 kg at 170 cm. Height in metres = 1.70, so BMI = 70 ÷ 1.70² = 70 ÷ 2.89 = 24.22. Body fat = 1.2 × 24.22 + 0.23 × 30 − 10.8 × 1 − 5.4 = 29.07 + 6.90 − 10.8 − 5.4 = 19.77, displayed as 19.8% body fat with the BMI input of 24.22 listed beneath. For a female with the same weight, height, and age the sex term is zero: 29.07 + 6.90 − 5.4 = 30.6%.
Weight is in kilograms and height in centimetres; the calculator divides height by 100 to get metres before squaring it. Convert pounds by dividing by 2.2046 and inches by multiplying by 2.54. Age is in years and shifts the estimate by 0.23 points per year. The output is a percentage of total body mass estimated to be fat, so 19.8% of 70 kg is about 13.9 kg of fat mass.
This is a screening figure, not a diagnosis. Population formulas do not account for build, muscle mass, age, pregnancy, ethnicity, or medical history, so an individual result can sit well outside the healthy band without indicating a problem, or inside it while one exists. Discuss anything that concerns you with a qualified clinician rather than acting on this number alone. On this page the figure rests entirely on weight, height, age and sex, so start there if the body fat percentage calculator returns something you did not expect.
Good to know: this is a population regression, not a measurement, and it inherits every weakness of BMI. Weightlifters and rugby players read high; frail or sarcopenic adults read low. It was derived from white Dutch adults aged 16 to 83 and may be biased in other ethnic groups, which later studies have documented. Entering height in inches or weight in pounds without converting produces an absurd BMI and body fat figure. A single reading is less informative than the trend across several months at the same time of day.
This is an educational screening estimate, not a diagnosis or a substitute for professional medical advice.
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How it works
Estimate body fat percentage from BMI, age, and sex. This tool explains the calculation so you can adjust the assumptions to match your situation.
Worked example
With Weight = 70 kg · Height = 170 cm · Age = 30 · Sex = male → 19.8 % body fat (BMI-based body fat estimate). Change an input above and this example updates with your numbers.
Common questions
Use the Deurenberg equation: body fat % = 1.2 × BMI + 0.23 × age − 10.8 × sex − 5.4, with sex as 1 for men and 0 for women. A man aged 30 with a BMI of 24.22 gets 29.07 + 6.9 − 10.8 − 5.4 = 19.8%. It is an estimate with a typical error of about 4 points.
Commonly cited ranges for adults put men at roughly 10–22% and women at 20–32%, rising modestly with age. These are not clinical thresholds; the American Council on Exercise and similar bodies publish descriptive categories rather than diagnostic cut-offs. A 30-year-old man at 19.8% falls within the typical range.
Only roughly. Deurenberg reported a standard error of about 4 percentage points, and the equation over-reads in muscular people and under-reads in those with low muscle. It is useful for a screening estimate or tracking change over time, not for judging an individual’s health. DXA or air-displacement testing gives a direct measurement.
Women carry more essential fat for reproductive function, so at the same BMI and age a woman has, on average, about 10.8 percentage points more body fat. The Deurenberg equation encodes that as a sex term rather than separate formulas; the 1.2 BMI slope and 0.23 age slope are shared.
On average, yes. Muscle mass tends to fall and fat mass rise with age even when weight is stable, which is why the equation adds 0.23 points per year. Between 30 and 50 that is 4.6 percentage points at the same BMI. Resistance training slows the shift. This is a screening estimate, not a diagnosis.