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Body Fat Calculator

US Navy body fat estimator based on circumference measurements. Free online Body Fat Calculator for health — instant, accurate results, no signup needed.

Navy method uses waist/neck/height (and hip for women).
Body fat %
16.1066%

Derivation

  1. ├── 01Givensex = male, h = 180, neck = 38, waist = 85, hip = 95
  2. ├── 02Formula{let t=e.sex,a=e.h,n=e.neck,r=e.waist,o=e.hip;return"male"===t?495 / (1.0324-.19077 × log₁₀(r-n)+.15456 × log₁₀(a))-450:495 / (1.29579-.35004 × log₁₀(r+o-n)+.221 × log₁₀(a))-450}
  3. ├── 03Substitute{let t=e.'male',a=e.180,n=e.38,r=e.85,o=e.95;return"male"===t?495 / (1.0324-.19077 × log₁₀(r-n)+.15456 × log₁₀(a))-450:495 / (1.29579-.35004 × log₁₀(r+o-n)+.221 × log₁₀(a))-450}
  4. └── 04Compute Body fat %16.106606
Did you know?

The US Navy body-fat equation (1984) uses only neck, waist (and hip for women) — developed so recruiters could assess fitness without specialist equipment.

§01What is

Understanding the Body Fat Calculator

The Body Fat Calculator computes Body fat % from 5 inputs: sex, height (cm), neck (cm), waist (cm), hip (cm, women only). US Navy body fat estimator based on circumference measurements.

Health metrics give us objective checkpoints against a body that can feel unreliable. Used alongside professional guidance — not in place of it — these numbers help you track progress and spot trends that matter. The Body Fat Calculator sits in that toolkit — it US Navy body fat estimator based on circumference measurements. Enter your numbers above and the result updates instantly; every step of the math is shown in the Derivation panel so you can see exactly how the answer was reached.

§02The Formula

How it’s calculated

{let t=e.sex,a=e.h,n=e.neck,r=e.waist,o=e.hip;return"male"===t?495 / (1.0324-.19077 × log₁₀(r-n)+.15456 × log₁₀(a))-450:495 / (1.29579-.35004 × log₁₀(r+o-n)+.221 × log₁₀(a))-450}

Where

sex
Sex — one of: male, female
h
Height (cm)
neck
Neck (cm)
waist
Waist (cm)
hip
Hip (cm, women only)
§03Practical Example

Step-by-step walkthrough

Scenario

Apply the formula to a realistic set of inputs: Sex = male, Height (cm) = 180, Neck (cm) = 38, Waist (cm) = 85, Hip (cm, women only) = 95.

  1. 01Start by noting the input — Sex: male (a category, not a number).
  2. 02Start by noting the input — Height (cm): 180.
  3. 03Start by noting the input — Neck (cm): 38.
  4. 04Start by noting the input — Waist (cm): 85.
  5. 05Start by noting the input — Hip (cm, women only): 95.
  6. 06Substitute these values into the formula: {let t=e.sex,a=e.h,n=e.neck,r=e.waist,o=e.hip;return"male"===t?495 / (1.0324-.19077 × log₁₀(r-n)+.15456 × log₁₀(a))-450:495 / (1.29579-.3500…
  7. 07Compute Body fat %: the calculator returns 16.1066.
  8. 08Cross-check the answer by opening the Derivation panel above — every line of math is shown so you can follow the computation end-to-end.
§04Variants

Common Body Fat Problems

The formula gets rearranged depending on which variable you need. Here are the patterns you’ll run into in the real world — find the one that matches your problem and follow the worked steps.

01 · PATTERN

Height (cm) halved

h = 90 (from 180)

Keep every other input at its default and halve the height (cm). See how body fat % responds.

  1. 01New Height (cm): 90
  2. 02Baseline Body fat %: 16.1066
  3. 03New Body fat %: 37.463
  4. 04Body fat % increases by 132.6% → use this sensitivity to plan for real-world variation.
02 · PATTERN

Height (cm) doubled

h = 360 (from 180)

Keep every other input at its default and double the height (cm). See how body fat % responds.

  1. 01New Height (cm): 360
  2. 02Baseline Body fat %: 16.1066
  3. 03New Body fat %: -3.45706
  4. 04Body fat % decreases by 121.5% → use this sensitivity to plan for real-world variation.
03 · PATTERN

Neck (cm) halved

neck = 19 (from 38)

Keep every other input at its default and halve the neck (cm). See how body fat % responds.

  1. 01New Neck (cm): 19
  2. 02Baseline Body fat %: 16.1066
  3. 03New Body fat %: 28.788
  4. 04Body fat % increases by 78.7% → use this sensitivity to plan for real-world variation.
04 · PATTERN

Neck (cm) doubled

neck = 76 (from 38)

Keep every other input at its default and double the neck (cm). See how body fat % responds.

  1. 01New Neck (cm): 76
  2. 02Baseline Body fat %: 16.1066
  3. 03New Body fat %: -37.1333
  4. 04Body fat % decreases by 330.5% → use this sensitivity to plan for real-world variation.
§05FAQ

Frequently asked questions

Yes. The calculator implements the standard formula as documented and returns exact floating-point results. No approximations are used unless noted in the formula.
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