Body Fat Calculator

This calculator uses the Deurenberg formula: Body Fat % = 1.20 x BMI + 0.23 x Age - 10.8 x gender - 5.4, where gender is 1 for men and 0 for women. A 70 kg, 1.75 m, 25-year-old man has an estimated body fat percentage of 16.98%. The formula was developed by Deurenberg, Weststrate, and Seidell (1991) from a large sample measured against underwater weighing, a reference-standard body composition method.

The American Council on Exercise (ACE) categories differ by gender: for men, roughly 2-5% is essential fat, 6-13% is typical of athletes, 14-17% is the fitness range, 18-24% is average, and 25% or higher is classified as obese; for women, the equivalent ranges are roughly 10-13%, 14-20%, 21-24%, 25-31%, and 32% or higher. Women require more essential fat than men for normal hormonal and reproductive function, which is why every category sits higher for women than for men.

A BMI-based estimate like the Deurenberg formula used here is reasonably accurate for the general population but less precise than direct measurement methods such as a DEXA scan, underwater weighing, or skinfold calipers, and it can meaningfully misjudge people who are unusually muscular or unusually sedentary for their weight, since it has no way to distinguish muscle from fat. Its advantage is that it needs no special equipment - only weight, height, age, and gender, all of which you likely already know.

Women naturally carry more essential fat than men at the same BMI and age, for hormonal and reproductive reasons, so the Deurenberg formula subtracts 10.8 percentage points for men and nothing for women. For the same 70 kg, 1.75 m, 30-year-old person, this is a difference of exactly 10.80 percentage points between the male result (18.13%) and the female result (28.93%) - not a rounding artifact, but a deliberate, fixed part of the formula.

The Deurenberg formula adds 0.23 percentage points of body fat per year of age, the opposite direction from BMR, which subtracts calories per year of age. Both reflect the same real phenomenon from different angles: as people age, they typically lose muscle mass and gain fat mass even at a stable weight, which lowers BMR (muscle burns more calories at rest than fat) while raising estimated body fat percentage. For a 70 kg, 1.75 m man, this calculator estimates 15.83% body fat at age 20 versus 29.63% at age 80, holding weight and height constant.

This calculator does not measure body fat independently of BMI - it computes your BMI first, using the same formula the BMI Calculator uses, and then adjusts it for age and gender to estimate body fat percentage. This means two people with the same BMI but different ages or genders will get different body fat percentage estimates here, even though the BMI Calculator itself would report them identically.

Yes - if you want a BMR estimate based on lean body mass rather than total weight (the Katch-McArdle method), calculate your body fat percentage here first, then multiply your weight by (1 - body fat percentage / 100) to get your lean body mass. The BMR Calculator and Calorie Calculator on this site use the Mifflin-St Jeor equation instead, which is based on total weight and does not require this extra step, but knowing your body fat percentage can make a manually-computed Katch-McArdle estimate more precise for people with unusually high or low muscle mass.

Yes - switch the calculator to US units and enter your weight in pounds and height in feet and inches instead of kilograms and metres. The values are converted to metric before the BMI and Deurenberg steps run, so the result matches what you would get entering the same measurements in metric. Switching the unit toggle also converts any figures you have already typed.

The U.S. Navy method estimates body fat from tape-measure circumferences (neck and waist for men, plus hip for women) rather than from BMI, so it responds to where you actually carry fat. This calculator uses the BMI-based Deurenberg formula instead, which needs only weight, height, age, and gender - no measuring tape - but cannot see body shape or tell muscle from fat. The Navy method is generally the more direct of the two field estimates; both are less accurate than a DEXA scan or hydrostatic weighing.

A DEXA (dual-energy X-ray absorptiometry) scan is the practical gold standard - it measures fat, lean mass, and bone directly and shows where fat sits, at the cost of a clinic visit. Hydrostatic (underwater) weighing is similarly accurate but needs a lab. Skinfold calipers and bioelectrical impedance (BIA) scales are cheaper and portable but more error-prone, and BIA in particular is thrown off by hydration, recent meals, and exercise. Any of these looks at your body more directly than a formula built on BMI.

For general health, most guidance points to roughly 10-20% for men and 18-28% for women - the athletes and fitness bands through the lower part of the average band. Below the essential-fat minimum (about 2-5% for men, 10-13% for women) is unsafe: it disrupts hormones, immune function, and bone health, and in women can stop menstruation. Well above the average band carries the same metabolic risks as excess weight in general. Where you aim within a healthy range is a personal choice, not a single correct number.