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Body fat calculator

The US Navy circumference method estimates body fat percentage from height, neck and waist measurements, adding hip circumference for women. A man of 180 cm with a 38 cm neck and 85 cm waist has an estimated 16.7% body fat, which falls in the fitness range. The method agrees with hydrostatic weighing to within about three percentage points.

Measured just below the larynx.

Men measure at the navel; women measure at the narrowest point.

Calculated in your browser — nothing is uploaded.

Result

Body fat — fitness

16.1%

495 ÷ (1.0324 − 0.19077·log₁₀(waist − neck) + 0.15456·log₁₀(height)) − 450

Category
Fitness
Fat mass
12.9 kg
Lean mass
67.1 kg

A male measuring 180 cm tall with a 38.0 cm neck and 85.0 cm waist has an estimated body fat of 16.1% by the US Navy circumference method, which falls in the "Fitness" range.

The US Navy circumference method estimates body fat to within about ±3 percentage points against hydrostatic weighing. DEXA remains the reference standard.

How to use the body fat calculator

  1. 01

    Select sex at birth

    The male and female equations use different coefficients, and the female formula additionally requires a hip measurement.

  2. 02

    Measure your neck

    Wrap a flexible tape just below the larynx, sloping slightly downward at the front. Keep the tape snug without compressing the skin.

  3. 03

    Measure your waist

    Men measure horizontally at the navel. Women measure at the narrowest point of the torso. Measure at the end of a normal exhalation, without pulling the tape tight.

  4. 04

    Measure your hips if applicable

    Women should measure the widest point of the hips and buttocks with the tape level all the way round.

  5. 05

    Read the estimate

    The result strip shows the body fat percentage and its descriptive category. Adding your weight also produces fat mass and lean mass in kilograms.

The formula

men:  495 ÷ (1.0324 − 0.19077·log₁₀(waist − neck) + 0.15456·log₁₀(height)) − 450
women: 495 ÷ (1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.22100·log₁₀(height)) − 450
waist
Waist circumference in centimetres — at the navel for men, at the narrowest point for women.
neck
Neck circumference in centimetres, measured just below the larynx.
hip
Hip circumference in centimetres at the widest point. Used in the female formula only.
height
Standing height in centimetres.
log₁₀
The base-10 logarithm.

The equation was derived by Hodgdon and Beckett at the Naval Health Research Center in 1984, regressed against hydrostatic weighing. It is the method the US Department of Defense uses for body composition assessment, which is why it is validated on a large and demographically broad sample.

Worked example

Sex
Male
Height
180 cm
Neck
38 cm
Waist
85 cm
Weight
80 kg
Result
16.7% body fat — fitness range

Subtract neck from waist: 85 − 38 = 47 cm. Take base-10 logarithms: log₁₀(47) = 1.67210 and log₁₀(180) = 2.25527. Substitute into the male equation: the denominator is 1.0324 − (0.19077 × 1.67210) + (0.15456 × 2.25527) = 1.0324 − 0.31899 + 0.34857 = 1.06198. Then 495 ÷ 1.06198 = 466.15, and subtracting 450 gives 16.7% body fat. At 80 kg that is 13.3 kg of fat mass and 66.7 kg of lean mass.

Frequently asked questions

What is a healthy body fat percentage?

The American Council on Exercise places men at 6 to 13% for athletes, 14 to 17% for fitness, 18 to 24% as average, and 25% or above as obese. For women the corresponding bands are 14 to 20%, 21 to 24%, 25 to 31%, and 32% or above. Women carry more essential fat for hormonal and reproductive function, which is why every band sits higher.

How accurate is the US Navy body fat formula?

The Navy circumference method agrees with hydrostatic weighing to within roughly ±3 percentage points for most adults. Accuracy declines at the extremes of body composition and for people whose fat distribution is unusual for their sex. Measurement technique is the largest source of error: a tape pulled tight or placed a few centimetres off shifts the result noticeably.

What is the most accurate way to measure body fat?

A four-compartment model combining hydrostatic weighing, deuterium dilution and DEXA is the research reference standard. In clinical practice, DEXA is the accepted benchmark, accurate to within 1 to 2 percentage points. Air-displacement plethysmography sits close behind. Bioelectrical impedance scales are the least reliable, being sensitive to hydration, recent meals and exercise.

Why does body fat matter more than weight?

Body weight combines fat, muscle, bone, organs and water, and cannot distinguish between them. Two adults of identical height and weight can differ by twenty percentage points of body fat. Health risk tracks fat mass and its distribution, particularly visceral fat around the organs, rather than total mass — which is exactly what BMI cannot see.

What is essential body fat?

Essential fat is the minimum required for normal physiological function, including nerve insulation, organ protection and hormone production. It is roughly 3 to 5% of body mass in men and 10 to 13% in women. Sustained levels below these thresholds impair immune function, bone density and reproductive hormone production.

Can body fat percentage change quickly?

Genuine change is slow, at roughly 0.5 to 1 percentage point per fortnight under a well-managed deficit. Larger day-to-day swings in any estimate reflect hydration, glycogen storage, food volume and measurement variation rather than tissue change. Measuring under identical conditions — same time of day, same tape, before eating — is what makes a trend interpretable.

Sources

Last reviewed: · Formula and sources verified by Syed Aqeel Ahmad Gillani. See the methodology for how every calculation is derived.

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