Body Fat Calculator

What is Body Fat Calculator?

A body fat calculator estimates the percentage of your total body weight that comes from fat tissue. Unlike the scale or BMI, body fat percentage reveals your actual body composition by separating fat mass from lean mass — muscle, bone, organs, and water.

Body fat includes essential fat, which you need to live, and storage fat under the skin and around organs. Too much storage fat raises the risk of heart disease and type 2 diabetes; too little disrupts hormones. Your percentage matters more for fitness goals than weight alone.

This calculator uses the U.S. Navy circumference method, developed by Hodgdon and Beckett at the Naval Health Research Center in 1984. It estimates body fat from neck, waist, and (for women) hip measurements plus height — no specialized equipment needed.

How to Use

1. Select your gender and unit system (metric or imperial).
2. Measure and enter your height, weight, waist (at the navel), and neck (just below the larynx).
3. If female, also enter your hip measurement at the widest point.
4. Click Calculate Body Fat to see your percentage, category, lean mass, and fat mass.

How to Take Accurate Measurements

Technique matters because the formula depends entirely on circumferences. Measure in the morning before eating, standing relaxed, with a flexible, non-stretch tape:

• Neck: wrap the tape just below the larynx (Adam's apple), sloping slightly downward toward the front. Keep your neck relaxed — do not flare the muscles.
• Waist: for men, measure horizontally at the navel; for women, at the narrowest point of the torso. Take the reading at the end of a normal exhale, and do not pull your stomach in.
• Hip (women only): measure around the widest point of the hips and buttocks with your feet together.
• Tape tension: the tape should lie flat and snug without compressing the skin. Measure to the nearest 0.5 cm or 1/4 inch, and never mix units.

The U.S. Navy Body Fat Formula

The Navy equations estimate body density from the ratio of your circumferences to your height, then convert it to a fat percentage. Two equivalent published forms exist: one for inches, one for centimeters.

For men (inches):

BFP = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76

For men (centimeters):

BFP = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450

For women, hip circumference is added to the waist before subtracting the neck:

BFP = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387 (inches)

BFP = 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450 (centimeters)

• BFP — body fat percentage, the result.
• waist, neck, hip — circumferences measured as described above.
• height — barefoot height, in the same unit as the circumferences.
• log10 — the base-10 logarithm.

Use one unit system throughout a formula. The calculator applies these equations for you and also derives fat mass (weight × BFP) and lean mass (weight − fat mass).

Worked Example

Take a man who is 70 inches tall, weighs 190 pounds, has a 36-inch waist, and a 15-inch neck:

1. Waist minus neck: 36 − 15 = 21 inches.
2. log10(21) ≈ 1.3222 and log10(70) ≈ 1.8451.
3. BFP = 86.010 × 1.3222 − 70.041 × 1.8451 + 36.76 = 113.72 − 129.23 + 36.76 ≈ 21.3%.

The metric form confirms it: with 70 in = 177.8 cm and 21 in = 53.34 cm, BFP = 495 ÷ (1.0324 − 0.19077 × log10(53.34) + 0.15456 × log10(177.8)) − 450 = 495 ÷ 1.0507 − 450 ≈ 21.1% — the small gap is just rounding between the two forms. At 190 pounds, his fat mass is roughly 40.4 lb (18.3 kg) and his lean mass about 149.6 lb (67.9 kg), placing him in the Average category for men.

Body Fat Percentage Categories

The American Council on Exercise (ACE) groups body fat into five categories — the same boundaries this calculator uses when it labels your result:

Women naturally carry more essential fat, so every category sits 8–12 points higher. Dropping below the essential range is dangerous — hormone production and organ protection suffer.

How Accurate Is the Navy Method?

The Navy method typically lands within 3–4 percentage points of laboratory techniques — excellent for tracking trends, though it can misjudge people whose fat distribution differs from the reference population, such as lean bodybuilders or adults over 60.

How it compares with the alternatives:

• DEXA scan: the clinical gold standard (within about 1–2%), but requires an appointment and costs $50–$150 per scan.
• Hydrostatic weighing: similarly accurate, but available only in labs.
• Skinfold calipers: comparable accuracy (±3–4%), but results depend heavily on the measurer's skill.
• Smart scales (bioelectrical impedance): convenient, but readings can swing 5% or more with hydration and meals.
• Navy tape method: free, fast, and highly repeatable — one of the best options for consistent home tracking.

Body Fat vs. BMI

Body mass index divides weight by height squared, so it cannot tell muscle from fat. A muscular athlete can be labeled "overweight" by BMI while sitting at 12% body fat, and a sedentary person can have a "normal" BMI while carrying excess fat — sometimes called "skinny fat." Body fat percentage measures composition directly, which is why the U.S. military uses the tape test for service members who exceed weight limits. Check your score with our BMI Calculator, then use this page to see what that weight is made of. If you are planning fat loss, pair the result with the TDEE Calculator to set a calorie target.

Frequently Asked Questions