How accurate is the Navy body-fat method?

The circumference method is typically within a few percentage points of more advanced techniques for average builds, but it can be off for very lean or very muscular bodies. Consistent measuring technique matters more than the absolute number for tracking change over time.

What is a healthy body fat percentage?

Ranges differ by sex. For men this tool labels up to 5% Essential, 6–13% Athletes, 14–17% Fitness, 18–24% Average, and above that Obese; for women the bands are 13, 20, 24, and 31%, reflecting higher essential fat needs.

What is the difference between fat mass and lean mass?

Fat mass is the total weight of body fat, while lean mass is everything else — muscle, bone, organs, and water. This calculator derives both by applying your body-fat percentage to your total weight.

Why does this differ from a BMI result?

BMI uses only height and weight and cannot distinguish muscle from fat. Two people with the same BMI can have very different body-fat percentages, which is why circumference-based estimates give a more complete picture.

Body Fat Calculator

Gender

Height

Weight

lbs

Waist

Neck

Body Fat17.4%

Fat Mass31.4 lbs

Lean Mass148.6 lbs

CategoryAverage

This calculator estimates your body fat percentage from tape measurements using the U.S. Navy circumference method, then splits your weight into fat mass and lean mass. Unlike BMI, which sees only height and weight, the circumference approach captures where you carry mass and classifies you from Essential Fat through Athletes, Fitness, Average, and Obese. It is a convenient at-home estimate rather than a lab-grade reading.

Formula

Female: %BF = 495 / (1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.22100·log₁₀(height)) − 450

waist: Waist circumference in cm (inches × 2.54)
hip: Hip circumference in cm (female formula only)
neck: Neck circumference in cm
height: Height in cm

How it works

Select your sex and enter height, neck, and waist in inches; women also enter hip circumference. Measurements are converted to centimetres (× 2.54) for the formula.
The Navy equations estimate body fat percent: men use waist minus neck, women use waist plus hip minus neck, each combined with height.
Your weight (converted to kg) is multiplied by the fat percentage to give fat mass, with the remainder as lean mass; both are shown in pounds, and your percentage is mapped to a category for your sex.

Worked example

A man 70 in tall, 180 lb, with a 34 in waist and 15 in neck.

Convert: waist 86.36 cm, neck 38.1 cm, height 177.8 cm.
%BF = 495 / (1.0324 − 0.19077·log₁₀(86.36 − 38.1) + 0.15456·log₁₀(177.8)) − 450 ≈ 17.4%.
Fat mass = 180 × 0.174 ≈ 31.4 lb; lean mass ≈ 148.6 lb.

Body fat ≈ 17.4% → Average; ~31.4 lb fat, ~148.6 lb lean.

Frequently asked questions

How accurate is the Navy body-fat method?: The circumference method is typically within a few percentage points of more advanced techniques for average builds, but it can be off for very lean or very muscular bodies. Consistent measuring technique matters more than the absolute number for tracking change over time.
What is a healthy body fat percentage?: Ranges differ by sex. For men this tool labels up to 5% Essential, 6–13% Athletes, 14–17% Fitness, 18–24% Average, and above that Obese; for women the bands are 13, 20, 24, and 31%, reflecting higher essential fat needs.
What is the difference between fat mass and lean mass?: Fat mass is the total weight of body fat, while lean mass is everything else — muscle, bone, organs, and water. This calculator derives both by applying your body-fat percentage to your total weight.
Why does this differ from a BMI result?: BMI uses only height and weight and cannot distinguish muscle from fat. Two people with the same BMI can have very different body-fat percentages, which is why circumference-based estimates give a more complete picture.

Related calculators

Army Body Fat Calculator BMI Calculator Lean Body Mass Calculator Healthy Weight Calculator