Body Fat Calculator

Estimate your body fat percentage using the US Navy circumference method and the BMI-based formula.

Last reviewed: June 2026
Built and maintained by · Last updated June 2026
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Body Fat % (Navy Method)
EssentialAthleticFitAverageAbove
Navy Method
BMI Method
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Fat Mass
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Lean Mass
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Looking for a quick BMI check? Try our BMI Calculator.

Quick Answer

This calculator estimates body fat percentage using the U.S. Navy method, which relies on tape measurements of your neck and waist — plus hips for women — along with your height. It is an estimate, not a clinical measurement like a DEXA scan. Enter your measurements above to get your estimated body fat percentage and category. Results are approximate and for general reference.

Important Disclaimer: This body fat calculator is an adult estimation tool. It is not a diagnosis, not an official military body composition assessment, and not a substitute for professional medical or nutrition advice. Pregnancy, adolescence, edema, unusual hydration status, physique competition, and eating-disorder concerns need clinician-guided interpretation.

How the Body Fat Calculator works

This calculator reports two separate estimates. The primary result uses a circumference method commonly called the US Navy method. Male mode uses height, waist, and neck circumference. Female mode uses height, waist, hip, and neck circumference. The BMI method is a second estimate based on BMI, age, and sex using the Deurenberg equation.

The Navy equations in this implementation use inch-based constants, so metric entries are converted to inches internally before the formula runs. For male mode, the calculator uses 86.010 x log10(waist - neck) - 70.041 x log10(height) + 36.76. For female mode, it uses 163.205 x log10(waist + hip - neck) - 97.684 x log10(height) - 78.387. Measurements are circumferences, not clothing sizes.

The BMI estimate uses body fat % = 1.20 x BMI + 0.23 x age - 10.8 x sex - 5.4, where sex is 1 for male and 0 for female in the original equation. It is included as a comparison because it uses different assumptions than the tape-measure method.

Interpreting the result

The category labels on this page are broad fitness reference labels, not clinical diagnoses. The most useful way to use a tape-based estimate is to measure consistently over time: same tape, same posture, same body locations, same time of day if possible, and no aggressive tape pulling. A single number can move several percentage points when the waist or neck measurement changes by a small amount.

Fat mass and lean mass are calculated from the Navy percentage and the weight you entered. Lean mass here means everything that is not estimated fat mass: muscle, bone, organs, water, connective tissue, and measurement error. It is not a direct muscle-mass measurement.

Worked examples

Default male entry: 5 ft 9 in, 170 lb, 15 in neck, and 34 in waist gives a Navy estimate of about 18.0%. The same default age and weight produce a BMI-method estimate near 20.8%, showing why the two methods should be compared as estimates rather than treated as exact measurements.

Metric equivalent: entering roughly 175 cm height, 77 kg weight, 38 cm neck, and 86 cm waist produces essentially the same Navy estimate because the calculator converts the metric circumferences to inches before applying the inch-based formula constants.

Female mode example: using 5 ft 9 in, 170 lb, 15 in neck, 34 in waist, and 38 in hip gives a Navy estimate near 26.9%. Hip circumference matters in female mode, so leaving an old default hip value in place can distort the result.

Common mistakes

  • Measuring the wrong location: use consistent neck, waist, and hip landmarks. A different waist landmark can change the estimate.
  • Pulling the tape tight: compressing skin or soft tissue makes the circumference smaller and biases the result.
  • Mixing methods: Navy and BMI estimates are not expected to match because they use different inputs and assumptions.
  • Using the result as a medical diagnosis: body composition can matter, but clinical risk depends on more than a tape estimate.
  • Using this for official military compliance: official assessments follow current service policy and measurement procedures, not this browser tool.

What this calculator does not do

It does not perform DEXA, Bod Pod, underwater weighing, MRI, skinfold caliper testing, or bioelectrical impedance analysis. It does not decide eligibility, diagnose obesity, prescribe a fat-loss target, measure visceral fat, or distinguish muscle from bone and water within lean mass.

Sources

This page is aligned with HPRC guidance on how military body composition is measured, CDC guidance on BMI as a screening measure, and the Deurenberg BMI body-fat prediction equation indexed by PubMed.

Frequently Asked Questions

It shows two estimates: a circumference estimate commonly called the US Navy method and a BMI-based Deurenberg estimate. The Navy method uses height, neck, waist, and for female mode, hip circumference. The BMI method uses BMI, age, and sex.
The displayed metric inputs are converted to inches before the Navy equations are applied because the hard-coded equations use inch-based constants. This keeps metric and imperial entries consistent.
No. It is an educational calculator. Official military body composition assessments use current service policy, trained measurement procedures, approved equipment, repeat measurements, and command-specific rules.
Tape-measure estimates can be useful for trend tracking, but they are sensitive to measurement landmarks, tape tension, posture, hydration, and body shape. They are not the same as DEXA, Bod Pod, underwater weighing, MRI, or a clinical assessment.
Pregnant people, teens, people with edema or unusual hydration status, competitive physique athletes, and anyone with medical or eating-disorder concerns should use clinician-guided assessment instead of relying on this calculator alone.