Body Fat Calculator (US Navy Method and BMI)

Body fat percentage from the US Navy tape method or a BMI estimate

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Updated 2026-10-04

The numbers already in the boxes (male, 175 cm, 75 kg, waist 85 cm, neck 38 cm, age 30) are an example. Replace them with your own measurements. Metric units only: cm and kg.

Sex

Height

Weight

Waist

Measured at navel height after a relaxed breath out.

Neck

Measure the narrowest part of the neck.

Result

Body fat: 16.9%
Fat mass: 12.7 kg
Lean mass (everything but fat): 62.3 kg
BMI: 24.5
Body surface area (Mosteller): 1.91 m²
Body surface area (DuBois): 1.9 m²

Waist check

A waist of 85 cm is below the abdominal obesity cut-off (90 cm).

Cut-off: Korean Society for the Study of Obesity guideline 2022 (men 90 cm, women 85 cm or more). PDF

Estimates can be off by several percentage points. This is not a clinical measurement.

The math with your numbers

495 ÷ (1.0324 − 0.19077 × log10(85 − 38) + 0.15456 × log10(175)) − 450 = 16.9%
Fat mass = 75 kg × 16.9% = 12.7 kg, lean mass = 75 − 12.7 = 62.3 kg
Mosteller √(175 × 75 ÷ 3600) = 1.91 m², DuBois 0.007184 × 75^0.425 × 175^0.725 = 1.9 m²

A rough estimate for reference only. It is not a diagnosis or treatment, so talk to a doctor if you are worried about your health. The tape method uses the 1984 US Navy report formula by Hodgdon JA and Beckett MB (coefficients from secondary literature, original not checked). The BMI method uses Deurenberg P et al., Br J Nutr 1991;65:105-114 (coefficients from secondary literature). Both can be off by several percentage points and do not replace a body composition scan or DEXA. They may not suit growing teens, pregnant women or very muscular people. Looked up 2026-10-04.

What it is

Body fat percentage is the share of your weight that is fat. Two people with the same weight can have very different amounts of muscle and fat, which is something BMI cannot show. This calculator lets you estimate it with just a tape measure and a scale. Choose the US Navy tape method or a BMI-based estimate, and you get body fat percentage, fat mass, lean mass, BMI, body surface area and a waist check in one place. Everything is calculated in your browser, and nothing you type is sent anywhere.

How to use

Pick a method. Use the tape method if you have a tape measure, otherwise the BMI estimate.
Enter sex, height in centimeters and weight in kilograms.
For the tape method add waist and neck, and hip as well for women. For the BMI method add your age.
Read the result table and the math lines to see how each number was reached.
The numbers already in the boxes are an example, so replace them with your own.

How it works

The tape method is the 1984 US Navy report formula by Hodgdon JA and Beckett MB. The coefficients come from secondary literature and the original was not checked. 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. All lengths are in cm.
The BMI method is Deurenberg P et al., Br J Nutr 1991;65:105-114, with coefficients from secondary literature: body fat % = 1.20 × BMI + 0.23 × age − 10.8 × sex (male 1, female 0) − 5.4.
Fat mass = weight × body fat %, and lean mass = weight − fat mass. Body surface area is shown twice, by Mosteller (√(height × weight ÷ 3600)) and DuBois (0.007184 × weight^0.425 × height^0.725).
Accepted ranges are height 100 to 250 cm, weight 30 to 300 kg, age 15 to 100 and circumferences 20 to 250 cm. If the formula result is below 2% or above 70% nothing is shown.
The waist check uses the Korean Society for the Study of Obesity guideline 2022: 90 cm for men and 85 cm for women.
Values are calculated as decimals and rounded once for display, to one decimal (two for surface area).

Examples

A man, 175 cm, 75 kg, waist 85 cm and neck 38 cm, with the tape method. These are example numbers.

Item	Math	Result
Body fat	495 ÷ 1.0601 − 450	16.9%
Fat mass	75 × 16.9%	12.7 kg
Lean mass	75 − 12.7	62.3 kg
BMI	75 ÷ 1.75²	24.5
Waist check	85 cm against 90 cm	below the cut-off

The BMI method for the same man at age 30 gives about 20.1%. A gap of a few percentage points between methods is normal.

Good to know

This is a rough estimate for reference only. It is not a diagnosis or treatment, so talk to a doctor if you are worried about your health. Time of day, hydration and how tight you pull the tape all move the result. Measuring the same way every time and watching the trend is more useful than trusting one number. Looked up 2026-10-04.

FAQ

How is body fat estimated here?

The tape method puts your height, waist and neck (plus hip for women) into the US Navy formula. The BMI method uses BMI, age and sex. A man of 175 cm with a waist of 85 cm and a neck of 38 cm comes out at about 16.9%.

Which method is more accurate?

The tape method uses your waist and neck, while the BMI method uses only height, weight and age. Which one fits better differs from person to person. Both can be off by several percentage points, so neither replaces a body composition scan or DEXA.

Why does it say the numbers cannot be calculated?

When the formula gives less than 2% or more than 70% the result is not realistic, so the tool refuses to show it. Re-measure your waist and neck in centimeters. Men need a waist larger than the neck, and women need waist plus hip larger than the neck.

What is the waist check based on?

The Korean Society for the Study of Obesity guideline 2022 calls a waist of 90 cm or more in men, or 85 cm or more in women, abdominal obesity. If you enter a waist, the tool compares it with that cut-off.

Can teens or pregnant women use it?

It is better not to. The formulas are for adults, and growth, pregnancy or very high muscle mass can make the error larger. Talk to a doctor if you are worried about your health.