Body Fat Calculator
Estimate your body fat two ways at once, the U.S. Navy tape method and a BMI-based number side by side so you can compare. Shows your category, BMI, and fat and lean mass. No sign-up.
- Free, no account
- No watermark
- No usage limit
About the Body Fat Calculator
Most body fat calculators hand you one number from one method and quietly let you believe it's precise. This one runs two at once and puts them side by side, the U.S. Navy tape method and a BMI-based estimate, so you can see how far apart they actually land, which is the honest part of the reading. Body fat read from a tape or a scale is always an estimate, and two methods bracketing your real figure tell you far more than a single number pretending to be exact.
There's a second reason for the pairing. The Navy method needs a tape measure around your neck and waist. The BMI-based estimate needs nothing but height, weight, and age, so with no tape in the house you still walk away with a real body fat percentage. Type in your weight and both estimates appear together, alongside your BMI, your category, and a fat and lean mass split. It all runs in your browser, so nothing is uploaded and nothing is logged, and your measurements stay on the device you typed them on so a refresh doesn't wipe them, which is where a number most people would rather not hand to a stranger's server belongs.
How to use it
- Pick your units. US (inches and pounds) or metric. The boxes relabel to match, and switching back keeps whatever you already typed.
- Choose your sex. The two sexes use different equations, and the female one needs a hip measurement the male one skips. Getting this right drives the whole result.
- Enter your age. It feeds the BMI-based estimate. The tape method ignores it.
- Measure and enter height, neck, and waist. Women add a hip. Wrap the tape snug but not biting into skin, keep it level, and read it at the end of a normal breath out. Don't suck in, that's the most common way people flatter their own number.
- Add your weight. This turns on the BMI-based estimate and the fat and lean mass split.
- Read both results. The Navy figure and the BMI figure sit next to each other, with the gap between them called out, your BMI underneath, and the mass split below that.
Measure twice, average the readings, and the number stays steady enough to track over weeks.
Two estimates, one screen
Here is why running both methods helps. The tape method reads your shape, the size of your waist against your neck, scaled to your height. The BMI method reads your overall heft, weight against height, then adjusts for age and sex using the Deurenberg formula. They come at the same question from different directions. If the two readings land close together, you can trust the number more. A wide gap between them is itself telling you something real about your body that a single-method calculator would hide.
The trained lifter is the classic case. Carry a lot of muscle and the BMI-based estimate reads high, because BMI can't tell dense muscle from fat. The tape method, reading your actual waist against a lean neck, usually comes in lower and closer to the truth. Seeing exactly where the two methods disagree is the whole point of showing them together.
Which number to trust
When they disagree, lean on the tape reading. The Navy circumference method was validated against lab measurements on a large population, and it separates fat from lean mass noticeably better than anything from BMI. The BMI-based figure is your sanity check and no-tape backup, it inherits BMI's blind spot for muscle, so treat it as a rough second opinion. For an average build, the two usually sit within a couple of points and either is fine.
Both are still estimates. For ground truth, a DEXA scan at a clinic runs forty to a hundred and fifty dollars and sets a real baseline. Get one once or twice a year to calibrate, then track weekly with this tool in between.
Reading your number: healthy ranges
A percentage means little without a map. These bands come from the American Council on Exercise, the reference most gyms and coaches quote:
| Category | Men | Women |
|---|---|---|
| Essential fat | 2 to 5% | 10 to 13% |
| Athletes | 6 to 13% | 14 to 20% |
| Fitness | 14 to 17% | 21 to 24% |
| Average | 18 to 24% | 25 to 31% |
| Obese | 25% and up | 32% and up |
Women's numbers run 7 to 8 points higher than men's in every band of that table. That's biology, they carry more essential fat, so a woman at 20% is about as lean as a man at 13%, both of them at the top of the athlete band. Never compare your figure straight across to the opposite sex.
Notice the essential fat floor, too, 2 to 5% for men and 10 to 13% for women. Dip below it and you are not lean but genuinely at risk, because very low body fat stalls hormones and hurts bone density. The target drifts up with age, so read the edges of the bands generously past 40.
Fat mass and lean mass
Enter your weight and the tool splits your bodyweight into fat and lean mass, using the tape estimate. Fat mass is your body fat percentage times your weight, lean mass is everything else, muscle, bone, organs, water.
This is where a plain bathroom scale can mislead you. Diet off six pounds while your body fat percentage barely moves, and the split shows a chunk of that loss was lean mass, a signal to eat more protein and lift. Train hard and the scale won't budge while fat mass drops and lean mass climbs. That's body recomposition, and going by the scale alone it would have looked like a failure.
Frequently asked questions
Which is more accurate, the Navy tape method or the BMI-based estimate?
The tape method, in almost every case. It reads your actual shape, so it tracks fat far better than a figure from weight alone. Independent studies put the Navy method within about 3 to 4 points of a DEXA scan for typical adults. The BMI-based number needs no tape, but it reads a muscular person as fatter than they are, so use it to confirm the tape reading, not overrule it.
I don't own a tape measure. Can I still get a body fat percentage?
Yes, and that's half the reason the BMI method is built in. Enter your height, weight, age, and sex, skip the neck and waist boxes, and you'll still get a body fat estimate from the BMI side alone. It's rougher than the tape reading, but it's a real figure you can get with a bathroom scale and nothing else. Pick up a cheap cloth tape later to sharpen it.
Why does the BMI-based estimate ask for my age but the tape method doesn't?
Because the Deurenberg formula behind it was fit with age as a variable, body fat tends to rise with age at the same BMI, so the equation nudges its answer up as you get older. The Navy method reads your measured shape directly and doesn't need that correction, which is why age never changes the tape number here. Leave age blank and only the tape estimate appears.
My two estimates are several points apart. Which one is right?
Trust the tape estimate and treat the gap as information. A wide spread almost always means you carry more or less muscle than average for your weight, exactly the situation BMI handles badly. Serious lifters see the BMI number sit well above the tape reading. Either way your true body fat is closer to the tape figure, and the distance is a hint about your build.
Is the BMI-based body fat number the same thing as my BMI?
No, they're different outputs. Your BMI is just weight over height squared, a single ratio with no direct read on fat. The BMI-based body fat estimate runs that BMI through a formula with your age and sex to guess a fat percentage. The tool shows both, so you see the raw ratio and the interpreted number in one place.
Can I share my result or come back to it later?
Yes. Hit Share and the tool copies a link with your exact inputs baked in, so you can send your setup to a coach or reopen it later right where you left off. Embed drops the live calculator onto your own site or blog, and your last entries are remembered in your browser between visits, with no account and no upload involved.
My waist came out smaller than my neck and I got an error. What happened?
The male tape formula subtracts your neck from your waist and then takes a logarithm, which only works when the waist is the larger figure. That error is nearly always a mix-up, the two got swapped, or one was typed in the wrong unit, inches into a centimeter box. Check that your waist really is the bigger number and both use the same units, then re-measure.