Body Fat Calculator
Body weight tells you how much you weigh. Body fat tells you what the weight is made of. This calculator uses the method the U.S. Navy built for fitness assessments: a tape measure around your neck and waist (and hips, for women) plus your height. No calipers, no scale that sends current through your feet.
It is an estimate, not a medical measurement. Against lab methods like DEXA it is typically off by about 3 to 4 percentage points, and the sections below say where it goes wrong and how to measure so it goes wrong less. Once you have a number, the Lean Body Mass Calculator and FFMI Calculator turn it into something you can train toward.
Feminine
Masculine
Your estimated body fat
Fitness range for men (ACE)
U.S. Navy circumference method (Hodgdon and Beckett, 1984)
28.2 lb fat mass
Body fat percent times your weight
147.8 lb lean mass
Everything that is not fat: muscle, bone, organs, water
12.5 to 19.5% likely range
The method is typically off by 3 to 4 points either way
- Essential fat Under 6
- Athletes 6 to 14
- Fitness 14 to 18
- Average 18 to 25
- Obese 25+
These are the American Council on Exercise ranges. They describe where a number sits in the population, not whether you are healthy: fitness and health depend on far more than one percentage.
- Lean Body Mass Calculator: what your lean mass means for protein and resting burn.
- FFMI Calculator: how much muscle you carry for your height.
- TDEE Calculator: turn this body fat into a calorie target (Katch-McArdle uses it).
A tape measure gives you one number with a 3 to 4 point error. A body scan reads one to three photos of your physique and returns body fat with a range, a physique score, lean mass and FFMI, region by region. Your first scan is free with an account.
Get your body scanThe equation is a function of three tape readings and your height. Most of the error you can control comes from where the tape sits.
Height
Barefoot, heels against a wall, looking straight ahead. Use the same height you would give a doctor, not the one you wish for: it goes into a logarithm, so a centimeter of vanity barely matters, but a typo of an inch or two does.
Neck
Tape just below the larynx (Adam's apple), sloping very slightly down toward the front. Look straight ahead, shoulders relaxed, and do not flare your neck forward or shrug. Men with a lot of neck muscle will read lower, which is the equation working as designed.
Waist (men)
Level with your navel, standing relaxed. Breathe out normally and read the tape at the end of the breath: no sucking in, no pushing out. Do not measure at the narrowest point, which is how the equation was built for men [1].
Waist (women)
At the narrowest point of the torso, usually between the ribs and the navel. If there is no clear narrowing, use the level of the navel. Relaxed, end of a normal exhale [2].
Hip (women)
Around the widest point of the buttocks, feet together, with the tape level all the way around. Check the tape in a mirror: it dips at the back more often than people think.
Every site
Snug on bare skin or thin clothing, not squeezing. Measure twice and use the average. A half-inch (about a centimeter) slip on the waist moves the answer by roughly a point, so take your time.
Hodgdon and Beckett fitted these equations in 1984 to men and women whose body fat had been measured by underwater weighing, and the Navy uses them because a tape measure is cheap and every recruit can be measured the same way [1][2]. Checked against DEXA in a 2023 study of Army trainees, the standard error of the estimate was about 3.4 points for men and 4.1 for women [3]. That is where the 3 to 4 point range on this page comes from.
It leans toward the middle
The same study notes the equations tend to read too low in people with higher body fat and too high in very lean people [3]. In that group the tape read about 6 points under DEXA at the start.
It is poor at short-term change
Over eight weeks of training, DEXA showed about 3 to 4 points of fat lost. The tape showed none for women and about 2 for men [3]. Do not use it to judge a single month of dieting: watch your waist, your weight trend and your lifts.
It cannot see your build
Circumferences stand in for fat. A thick neck from muscle, or a waist that is wide for another reason (a large frame, a full stomach), will fool it. A scan that looks at your physique directly sidesteps that, which is why we built one.
The categories are the American Council on Exercise ranges [4]. They describe where a reading sits among people, not your health.
Compare with yourself, not with a stranger
The number is useful as a rough position and as a repeat reading under the same conditions: same tape, same sites, same time of day. Read it as a range, not a point.
Do not chase the bottom of a range
Essential fat is the minimum the body needs to function, not a target. Staying near it for long can cost you hormones, bone and energy. Most people training for strength and health feel best in the athletes or fitness ranges.
Check it with something else
If the tape says one thing and the mirror, your lifts and your waist trend say another, believe the pile of evidence. Skinfolds, DEXA or a photo scan are other angles on the same question.
Want calories to match? Your body fat feeds the Katch-McArdle equation in the BMR Calculator and the TDEE Calculator.