Body Fat Calculator
This free body fat calculator estimates your body fat percentage using the US Navy method, from your height plus a few tape-measure circumference measurements. It shows your percentage and category instantly, and optionally your fat mass and lean mass if you enter a weight. Nothing you enter is sent anywhere or stored.
How to Use It
- Choose your gender and US / Imperial or Metric units.
- Enter your height, neck, and waist measurements (plus hip, if Female).
- Optionally enter your weight to also see fat mass and lean mass.
- Your body fat percentage and category appear instantly as you type.
How It Works
The US Navy method estimates body fat percentage from circumference measurements rather than weighing you, which is what lets it distinguish fat from lean mass in a way a bathroom scale or BMI calculation cannot. For men, it uses waist and neck measurements plus height. For women, it adds a hip measurement, since the formula itself is derived differently for each sex, not just adjusted afterward.
Formulas
men: body fat % = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76
women: body fat % = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387
all measurements in inches
A worked example: a man who is 5'10" (70 inches) tall, with a 15 inch neck and a 34 inch waist, comes out to 17.51% body fat, in the "Fitness" category on the table below. The same height and neck measurement with a larger, 38 inch waist instead comes out to 24.65%, in the "Average" category, since a larger waist relative to neck and height is exactly what the formula reads as more body fat.
| Category | Men | Women |
|---|---|---|
| Essential Fat | Below 6% | Below 14% |
| Athletes | 6% to 13.9% | 14% to 20.9% |
| Fitness | 14% to 17.9% | 21% to 24.9% |
| Average | 18% to 24.9% | 25% to 31.9% |
| Obese | 25% and above | 32% and above |
This is the American Council on Exercise (ACE) scale, the most commonly cited body fat category chart, not a universal medical standard. Different organizations publish slightly different cutoffs.
Everything runs client-side in your browser. No measurements you enter are sent anywhere or stored.
Frequently Asked Questions
Why does this use a tape measure instead of a body composition scale or calipers?
This calculator uses the US Navy method, which estimates body fat from a few circumference measurements (neck, waist, and for women, hip) plus height. It's one of the most widely used tape-measure methods because it needs no special equipment, just a flexible tape measure, unlike skinfold calipers (which take practice to use consistently) or a body composition scale (which estimates fat through a small electrical current and can vary with hydration level).
How much does measurement technique affect the result?
A fair amount. Wrap the tape snugly but not pulled tight, keep it level and parallel to the floor, and measure at the same spot each time (waist at the navel, neck just below the larynx). A tape pulled too tight or measured at an inconsistent spot can shift the result by several percentage points, so if you're tracking change over time, try to measure the same way each time more than getting any single measurement perfect.
Why is the category scale different for men and women?
Because a healthy amount of essential body fat genuinely differs by sex. Women's bodies carry more essential fat than men's (related to hormonal and reproductive function), so the same percentage that would be unusually low for a woman is a normal, healthy level for a man. The category table below uses separate scales for exactly this reason, not because the measurement method itself works differently.
How is this different from the BMI Calculator?
BMI only uses height and weight, and can't distinguish fat from muscle, a muscular athlete and a sedentary person of the same height and weight get the identical BMI. This calculator estimates actual body composition from tape measurements, so it can tell those two people apart in a way BMI structurally cannot. Neither one is a clinical-grade measurement, but this one is a closer estimate of body fat specifically.
Why do I need to enter my hip measurement, and only if I select Female?
The Navy method's formula for women includes hip circumference as one of its terms; the formula for men does not. This isn't an oversight, it's a real difference in how the two formulas were derived, so the Hip field only appears when it's actually used in the calculation.
Is a tape-measure estimate as accurate as a DEXA scan?
No. DEXA scans and hydrostatic (underwater) weighing are the clinical gold standards for body composition, but both require specialized equipment you won't have at home. The Navy method is a well-studied, reasonably close estimate for most people, typically within a few percentage points of a clinical measurement, which makes it a practical stand-in, not a replacement, for an actual clinical test.
What do fat mass and lean mass mean in the results?
Fat mass is your body weight multiplied by the estimated body fat percentage, the portion of your weight that is fat. Lean mass is everything else (muscle, bone, organs, water), calculated as your total weight minus fat mass. Both only appear if you enter a weight, since the percentage itself does not require one.