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The calculator applies the U.S. Navy circumference equations from Hodgdon and Beckett (1984). Your centimetre measurements are converted to inches, then the male formula uses waist, neck and height while the female formula adds hip circumference to capture typical female fat distribution. The result is your estimated body fat percentage, classified into one of five ACE categories: essential fat, athletes, fitness, average, or obese. The method carries roughly 3 to 4 percentage points of error versus laboratory scans, so treat the number as a tracking estimate. Results are estimates for fitness planning, not professional medical advice.
The U.S. Navy circumference method (Hodgdon-Beckett, 1984) estimates body fat from tape measurements using the logarithmic relationship between body circumferences and body density:
Men: BF% = 86.010 × log10(waist - neck) - 70.041 × log10(height) + 36.76
Women: BF% = 163.205 × log10(waist + hip - neck) - 97.684 × log10(height) - 78.387
The equations were fitted to measurements in inches, so this calculator converts your centimetre inputs to inches before applying them. Worked example: a man with waist 85 cm, neck 38 cm, height 178 cm converts to 33.46, 14.96 and 70.08 inches: 86.010 × log10(18.50) - 70.041 × log10(70.08) + 36.76 = about 16.5%. The log10 terms capture how body density changes as circumferences grow relative to height.
The formula is only as accurate as your measurements. Use a flexible, non-stretch tape and follow this protocol to measure your body fat at home:
Neck: just below the larynx (Adam's apple), perpendicular to the neck's axis. Look straight ahead, keep the tape snug but not compressing the skin.
Waist: men at the level of the navel, women at the narrowest point of the abdomen. Keep the tape horizontal, measure at the end of a normal exhale, relaxed, not sucking in.
Hip (women): at the widest point of the hips and buttocks, tape horizontal, feet together.
Height: barefoot, standing tall.
Measure on bare skin, take each reading two or three times and average them, and measure in the morning before eating for consistency.
The American Council on Exercise (ACE) defines five adult body fat categories, the standard body fat percentage chart used in fitness:
Essential fat: 2-5% men, 10-13% women. The minimum needed for organ function; not a sustainable target.
Athletes: 6-13% men, 14-20% women. Typical of competitive athletes.
Fitness: 14-17% men, 21-24% women. Associated with an active, health-conscious lifestyle.
Average: 18-24% men, 25-31% women. Typical of the general population.
Obese: 25%+ men, 32%+ women. Elevated cardiometabolic risk.
Women naturally carry more body fat than men at equivalent fitness levels due to hormonal and reproductive physiology, which is why the thresholds differ. Healthy ranges also rise with age as lean mass declines, so treat the table as a guide and track your own trend over time.
BMI only knows your height and weight, so it cannot tell muscle from fat: a muscular athlete can read as overweight on BMI while staying lean. Body fat percentage looks past total weight to actual composition, which is why athletes and regular gym-goers find it a more honest measure. Conversely, a sedentary person with a normal BMI of 22 can carry 28% body fat, sometimes called normal-weight obesity, with elevated metabolic risk despite a normal weight. For a quick population-level screen, BMI is still handy; for a personal fitness read, body fat percentage is better. Pair the two for the fullest picture.
Studies put the Navy method's standard error around 3 to 4 percentage points versus DEXA, the laboratory gold standard, and it correlates strongly with hydrostatic weighing (about r = 0.90 for men, 0.85 for women). That makes it more accurate than BMI-based estimates and far easier than skinfold calipers, which need trained technique. But the error is not random for everyone: very muscular people read artificially high because the tape cannot distinguish muscle from fat, and older adults with muscle loss can read low. For tracking changes over time, the method is excellent, provided you use the same protocol every time. For a single precise number, a DEXA scan is the reference. Results here are estimates for fitness tracking, not professional medical advice.
Select your gender, enter your height, neck and waist in centimetres, and hip too if you are female, to calculate your body fat percentage. The calculator converts everything to inches, applies the Navy equations, and returns your estimated body fat percentage plus your ACE category. Measure consistently: same tape, same time of day, same conditions, and compare readings monthly rather than daily, since hydration and food swing results by a point or two.
Body fat percentage is the proportion of your total body weight made up of fat tissue. A person weighing 80 kg with 20% body fat carries 16 kg of fat and 64 kg of lean mass (muscle, bone, water, organs). It is a more meaningful fitness and health metric than weight alone, because weight cannot tell fat from muscle.
The U.S. Navy circumference method, developed by Hodgdon and Beckett in 1984 and validated against hydrostatic weighing. It uses neck, waist, and for women hip circumferences alongside height, entered in centimetres and converted to inches internally: men 86.010 × log10(waist - neck) - 70.041 × log10(height) + 36.76; women 163.205 × log10(waist + hip - neck) - 97.684 × log10(height) - 78.387.
About 3 to 4 percentage points of error versus DEXA scans, the gold standard. It is more accurate than BMI for body composition and much easier than skinfold calipers. The main error sources are inconsistent measurement technique and atypical fat distribution. It is excellent for tracking trends over time, less reliable as a single absolute number.
Men and women store fat differently: men store it predominantly around the abdomen, which the waist measurement captures, while women store more in the hips and thighs. The female Navy equation adds hip circumference to capture that typical distribution, which is why the hip input only applies to women.
For muscular or very lean people, yes: BMI cannot distinguish muscle from fat, so a fit person can read as overweight on BMI. Body fat percentage measures composition directly. For a quick population screen, BMI is still handy. Pairing both gives the fullest picture.
Monthly, or every 4 to 6 weeks. Daily or weekly readings fluctuate too much from hydration, food, and time of day to be useful. Measure under the same conditions each time, morning before eating, and watch the trend over 2 to 3 months rather than obsessing over a single reading.
No. Pregnancy changes circumference readings in ways the equations were not designed to handle, so the estimate would be meaningless. The equations were also derived from adult Navy personnel and do not apply to children. Use a different method or wait until after delivery.
It is less accurate for very muscular athletes: the circumference method cannot distinguish subcutaneous fat from muscle, so a bodybuilder can read artificially high. For lean athletes with low muscle mass it may read low. The standard error of about 3 to 4% applies to a general population, not extreme body types. Results are estimates, not professional medical advice.
No. Fat loss is systemic: genetics and hormones determine where fat comes off first, and training one area strengthens the muscle underneath without preferentially burning the fat on top. A moderate calorie deficit, high protein, and resistance training 3 to 4 times a week are what actually lower body fat percentage.