Body Fat Percentage Calculator

This calculator estimates body fat percentage using the US Navy method, which works from circumference measurements rather than equipment. Men supply neck and waist measurements, women neck, waist and hips. The formula, also known as the Hodgdon equation, uses the logarithmic relationship between those circumferences and your height. For men it is 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76, and for women 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387.

Measuring technique decides how useful the answer is. Take the neck at its narrowest point, the waist at the navel for men or at the narrowest point for women, and the hips at their widest. Measure on bare skin, standing relaxed, ideally in the morning before eating. Done that way the Navy method comes within roughly 3 to 4% of a DEXA scan, which is why the US and UK military use it for fitness screening, since a tape measure is cheap and consistent.

Healthy ranges differ by sex and by what you are asking of your body. Broadly, 10 to 20% is healthy for men and 18 to 28% for women. Essential fat, below which health suffers, sits at around 3 to 5% for men and 10 to 13% for women. Working through the fuller bands used by the NHS and the American Council on Exercise, athletes come in at 6 to 13% for men and 14 to 20% for women, the fitness range is 14 to 17% and 21 to 24%, average is 18 to 24% and 25 to 31%, and obesity begins at 25% and 32%. Women naturally carry more fat because of oestrogen and reproductive biology.

A single number can mislead badly if you pick the wrong one. A muscular rugby player of 100kg at 1.85m has a BMI of 29.2, which reads as overweight, yet might be at 12% body fat, which is elite. That gap is exactly why circumference-based estimates exist. The Navy method is most reliable for adults aged 18 to 50 and least reliable for the very muscular, where the waist measurement understates how much of the mass is lean.

Accuracy varies enormously between methods, and so does the price. A DEXA scan is the practical gold standard at 1 to 2% and £80 to £150 at private clinics. Hydrostatic weighing manages 2% in sports science labs, and BodPod air displacement 2 to 3% in NHS hospitals and some gyms. Skinfold callipers over 3 to 7 sites give 3 to 5% in skilled hands. Bioelectrical impedance in gym and smart scales drifts to 5 to 10% depending on hydration, tape measure methods such as the Navy and YMCA formulas to 5 to 8%, and visual estimation to 10%. Callipers and a spreadsheet make the best home option, though the technique takes practice.

Where the fat sits matters as much as how much there is. Subcutaneous fat under the skin, particularly on hips, thighs and buttocks, is largely a cosmetic question. Visceral fat around the liver, intestines and pancreas is strongly linked to type 2 diabetes, heart disease, fatty liver and stroke. Waist circumference is the best home proxy, and the NHS targets are under 94cm for men, with 102cm counting as high risk, and under 80cm for women, with 88cm high risk. A waist-to-height ratio under 0.5 is the simple version, so keep your waist less than half your height.

Reducing body fat safely runs at 0.5 to 1% a month. A deficit of 500 kcal a day loses about 0.5kg a week and 1,000 kcal a day about 1kg, which the NHS treats as the upper limit. Protein of 1.6 to 2.2 g per kg of body weight during a deficit is what preserves muscle, and without resistance training 25 to 50% of the weight you lose can be muscle rather than fat. Cardio burns energy but will not change body composition on its own. Sleep of 7 to 9 hours matters too, since under 6 hours drives cortisol and with it visceral fat storage.