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Body Fat Calculator

Estimate your body fat percentage with the U.S. Navy tape method, see your body-fat category, fat mass, lean mass, and how you compare to the ideal for your age — in US or metric units.

Gender
years
lb
ft
in
in

Measured just below the larynx.

in

Men: at the navel. Women: at the smallest width.

in

Women only — measured at the largest width. Required for the female Navy formula.

Body Fat (U.S. Navy)

Athletes

11.1%

Body Fat Mass
18.3 lb
Lean Body Mass
146.7 lb
Ideal Body Fat for Your Age
10.5%
Body Fat to Lose to Reach Ideal
1.0 lb
Body Fat (BMI method)
18.0%
Body Fat (U.S. Navy)11.1 %View results

This calculator estimates your body fat percentage from a few tape measurements using the U.S. Navy circumference method, then reports your body-fat category, fat mass, lean mass, and how you compare to the ideal for your age. Body fat percentage is often a better health signal than weight or BMI alone because it separates fat from muscle and bone.

Formula

The U.S. Navy method uses log-transformed circumference measurements. The imperial (inches) formulas are:

Men:   %fat = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76
Women: %fat = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387

Fat mass is %fat × weight, and lean body mass is weight − fat mass. The metric (cm) variants use a slightly different equation, which is why switching units can change the result by a fraction of a percent.

The BMI-method estimate shown alongside the result uses only BMI and age, so it can't tell muscle from fat. Treat it as a rough sanity check, not a second measurement.

Body fat categories (American Council on Exercise)

CategoryWomenMen
Essential fat10–13%2–5%
Athletes14–20%6–13%
Fitness21–24%14–17%
Average25–31%18–24%
Obese32%+25%+

Examples

Man, 5 ft 10 in, 165 lb, neck 18 in, waist 34 in

log10(34 − 18) = 1.204 and log10(70) = 1.845, so %fat = 86.010 × 1.204 − 70.041 × 1.845 + 36.76 ≈ 11.1% — within the "Athletes" range. Fat mass is about 18.3 lb and lean mass about 146.7 lb.

Woman, 165 cm, 60 kg, neck 32 cm, waist 70 cm, hip 95 cm

Using the metric women's formula, %fat ≈ 24.9% — the "Fitness" range — with roughly 14.9 kg of fat mass.

Frequently asked questions

How accurate is the U.S. Navy body fat method?
The Navy circumference method is typically within about 3–4 percentage points of a hydrostatic (underwater) weighing for most people. It's far more convenient than lab testing, but it's an estimate — measurement technique matters, and it's less reliable for very lean or very obese bodies. For clinical accuracy, use DEXA, hydrostatic weighing, or bioelectrical impedance.
How do I measure my neck, waist, and hip?
Use a flexible tape, snug but not compressing the skin, and measure to the nearest quarter inch (0.5 cm). Neck — just below the larynx, sloping slightly down to the front. Waist — men measure at the navel, women at the narrowest point. Hip (women) — at the widest point of the buttocks.
Why does the calculator ask for hip only for women?
The U.S. Navy formula for women includes the hip circumference because fat distribution differs by sex; the men's formula uses only waist and neck. If you select male, the hip field is ignored.
What is a healthy body fat percentage?
It depends on sex and goals. The American Council on Exercise considers 14–24% healthy for men and 21–31% for women, with athletes lower. Essential fat (the minimum the body needs) is about 2–5% for men and 10–13% for women.
What is the difference between the Navy method and the BMI method?
The Navy method estimates body fat from body measurements (neck, waist, hip, height). The BMI method estimates it from your BMI and age alone, so it can't account for build or muscle — it's shown here only as a rough cross-check.

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