Body Fat Calculator

Estimate your body fat percentage with a tape measure — the US Navy circumference method

Measurements (US Navy Method)

Sex

Units

Height (in)

Neck (in)

Below the larynx

Waist (in)

At the navel

Weight (lb)

For the fat/lean split

Estimate only: The Navy circumference method is typically within ±3–4% of DEXA scans. Measure with a flexible tape, snug but not compressing the skin, and use consistent conditions (morning, before eating) when tracking changes.

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Quick summary

Measure your neck and waist (plus hips for women) with a tape measure, add your height, and the US Navy circumference equations estimate your body fat percentage. Results are compared with American Council on Exercise (ACE) ranges: for men, 6–13% is athletic and 18–24% average; for women, 14–20% athletic and 25–31% average. It is an estimate, less precise than lab methods such as DEXA, but useful for tracking change over time.

Reviewed by Simple Calculators TeamLast reviewed July 12, 2026

For information only — not medical advice. Results are estimates from published formulas and can't account for your health history. Talk to a doctor or other qualified clinician before making health decisions.

How to use this calculator

Choose your Sex and Units (Imperial in, lb or Metric cm, kg); women will also see a Hip field.
Enter your Height, then measure your Neck just below the larynx (Adam's apple) with a flexible tape.
Measure your Waist at the navel for men, or at the narrowest point for women, with the tape level and snug but not compressing the skin.
Women: measure your Hip at the widest point of the buttocks. Everyone: enter your Weight, which is used only to split fat mass from lean mass.
Read your Estimated Body Fat percentage, fat and lean mass, and the ACE category table. Re-measure under the same conditions every few weeks and watch the trend rather than any single reading.

Body Fat Formulas

US Navy Body Fat Formula (Men)

\%BF = 86.010 \times \log_{10}(waist - neck) - 70.041 \times \log_{10}(height) + 36.76

waist: Waist circumference at the navel, in inches (cm ÷ 2.54)
neck: Neck circumference just below the larynx, in inches
height: Height in inches

Worked example

Man, 70 in tall, neck 15 in, waist 34 in, weight 180 lb

Given: waist = 34 in
neck = 15 in
height = 70 in
weight = 180 lb
Calculation: $\%BF = 86.010 \times \log_{10}(19) - 70.041 \times \log_{10}(70) + 36.76 = 109.986 - 129.233 + 36.76$
Result: Body fat ≈ 17.5% (fat mass 31.5 lb, lean mass 148.5 lb)

US Navy Body Fat Formula (Women)

\%BF = 163.205 \times \log_{10}(waist + hip - neck) - 97.684 \times \log_{10}(height) - 78.387

waist: Waist circumference at the narrowest point, in inches (cm ÷ 2.54)
hip: Hip circumference at the widest point, in inches
neck: Neck circumference just below the larynx, in inches
height: Height in inches

Worked example

Woman, 65 in tall, neck 13 in, waist 28 in, hip 38 in, weight 140 lb

Given: waist = 28 in
hip = 38 in
neck = 13 in
height = 65 in
weight = 140 lb
Calculation: $\%BF = 163.205 \times \log_{10}(53) - 97.684 \times \log_{10}(65) - 78.387 = 281.410 - 177.093 - 78.387$
Result: Body fat ≈ 25.9% (fat mass 36.3 lb, lean mass 103.7 lb)

Frequently asked questions

How is body fat percentage calculated?

This calculator uses the US Navy circumference method, which estimates body fat from height and tape measurements. For men it uses the base-10 logarithm of waist minus neck and of height; for women it uses waist plus hip minus neck and height. Measurements are converted to inches first. Your weight is then split into fat mass and lean mass using the resulting percentage.

How accurate is the Navy body fat method?

The Navy method gives a reasonable estimate, but it is less precise than lab methods like DEXA, and errors of a few percentage points are common. It can be further off for very muscular or very lean people, and small measuring errors change the result. Its real strength is tracking change: measure the same way every few weeks and the trend is more reliable than any single number.

What is a healthy body fat percentage?

There is no single ideal number, but the ACE ranges used here give a guide. Men: essential fat 2–5%, athletes 6–13%, fitness 14–17%, average 18–24%, obese 25% or more. Women carry more essential fat: essential 10–13%, athletes 14–20%, fitness 21–24%, average 25–31%, obese 32% or more. Health risks rise mainly at the higher end; a doctor can put your number in context.

How do I measure correctly?

Use a flexible tape, snug but not compressing skin, and keep it level. Neck: just below the larynx, sloping slightly down to the front. Waist: at the navel for men, at the narrowest point for women. Hips (women): at the widest point. Measure in the morning before eating, take each measurement twice, and repeat under the same conditions each time.

Why do women need a hip measurement?

Women need a hip measurement because the Navy formula for women uses waist plus hip minus neck. Women typically store more fat around the hips and thighs, so including the hip girth makes the estimate more representative. The men's formula uses only waist and neck, because men tend to store more fat around the abdomen. That is why the Hip field appears only when you select Female.

Why does body fat matter more than BMI?

Body fat percentage tells you what your weight is made of, which BMI cannot. A muscular 5 ft 10 in, 200 lb lifter and a sedentary person of the same size share a BMI of 28.7 but have very different body compositions. Body fat measures what BMI only approximates. Use both: BMI for quick screening, body fat percentage for body composition.

What are fat mass and lean mass?

Fat mass is the weight of fat in your body, and lean mass is everything else, including muscle, bone, organs, and water. The calculator finds fat mass by multiplying your weight by your body fat percentage, then subtracts it from your weight to get lean mass. For example, 180 lb at 17.5% body fat is 31.5 lb of fat mass and 148.5 lb of lean mass.

Key terms

Circumference Method: Estimating body fat from girth measurements — the Navy version uses neck, waist, height (and hip for women).
DEXA Scan: Dual-energy X-ray absorptiometry — the clinical gold standard for body composition, against which tape methods are validated.
Essential Fat: The minimum fat needed for normal physiology — about 2–5% for men and 10–13% for women.
Lean Mass: Everything that isn't fat: muscle, bone, organs, water. Total weight × (1 − body fat %).

Methodology, sources & limitations

This page shows the formula, assumptions, and limitations used for this estimate. Rates, thresholds, and other time-sensitive inputs can change, so verify them against the relevant official source before relying on a result.

For our review approach and the primary sources we consult, see the methodology and source policy. If you spot an outdated figure or formula, please contact us with a correction.

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