Body Fat Calculator
Professional body fat calculator using the U.S. Navy circumference method and Deurenberg BMI estimate. Mobile-first, accessible, and accurate.
Measurement & Method
Switch units, select the preferred method, and tell us your sex to unlock the right equation.
Use the Navy equations for circumference-based data. Provide weight and age for the BMI estimate to unlock mass outputs.
How to Use This Calculator
This professional-grade tool estimates your body fat percentage using two validated approaches: the U.S. Navy circumference method (measurement-based, recommended) and the Deurenberg BMI-based estimate (useful when tape measurements are unavailable). It’s designed for accuracy, accessibility, and mobile use.
Data Source & Methodology
Authoritative Data Sources:
- Hodgdon JA, Beckett MB. Prediction of Percent Body Fat for U.S. Navy Men and Women from Body Circumferences and Height. NHRC Report 84-11, Naval Health Research Center, San Diego, 1984. Direct PDF.
- Deurenberg P, Weststrate JA, Seidell JC. Body mass index as a measure of body fatness in adults. Br J Nutr. 1991;65(2):105–114. DOI:10.1079/BJN19910073.
All calculations are strictly based on the formulas and data provided by these sources.
Measurement Guidance
- Height: Stand tall without shoes. For US units, enter height in inches (e.g., 71). Use the tip of a ruler or wall-mounted tape for accuracy.
- Neck: Measure just below the larynx (Adam’s apple) with the tape slightly angled down across the front. Keep the tape snug but not compressing the skin.
- Waist: Measure horizontally at the level of the navel, with the abdomen relaxed and at the end of a normal exhale.
- Hips (women): Wrap the tape around the fullest part of the buttocks with the tape level and snug.
- Age: Required only for the BMI-based Deurenberg estimate; it is not used in the Navy method.
- Weight: Optional but necessary to calculate fat mass, lean mass, and a BMI estimate.
Methodology
The Navy equations compute body fat percentage from circumference data, converting all measurements to inches before applying the formulas below. When only height, weight, and age are available, the Deurenberg BMI-based estimate provides a reasonable alternative (especially for quick tracking), though it may be biased for muscular builds.
How It Works: A Step-by-Step Example
Scenario: Male, Metric units, Height 180 cm, Neck 38 cm, Waist 85 cm, Weight 80 kg.
- Convert to inches for the Navy formula: height 180 ÷ 2.54 ≈ 70.87 in; neck 38 ÷ 2.54 ≈ 14.96 in; waist 85 ÷ 2.54 ≈ 33.46 in.
- Compute logarithms: log₁₀(33.46 - 14.96) ≈ 1.267; log₁₀(70.87) ≈ 1.851.
- Apply the formula: %BF = 86.010 × 1.267 - 70.041 × 1.851 + 36.76 ≈ 15.3%.
- Fat mass: 0.153 × 80 kg ≈ 12.2 kg; Lean mass: 80 - 12.2 ≈ 67.8 kg.
Glossary of Variables
| Field / Result | Definition |
|---|---|
| Units | Choose Metric (cm, kg) or US (in, lb) for each measurement. |
| Method | U.S. Navy (measurement-based) or BMI estimate (weight, height, age). |
| Sex | Essential to select the appropriate equation and category thresholds. |
| Age | Used only in the BMI estimate. |
| Height | Stature without shoes. |
| Neck | Neck circumference just below the Adam’s apple. |
| Waist | Abdominal circumference at the navel. |
| Hip | Widest hip/buttocks circumference (women only). |
| Weight | Body mass; enables fat and lean mass outputs along with the BMI estimate. |
| Body fat % | Proportion of body weight made up of fat tissue. |
| Fat mass | Body fat % multiplied by body mass (kg). |
| Lean mass | Body mass minus fat mass (fat-free mass). |
| Category | Classification using ACE ranges: Essential, Athlete, Fitness, Acceptable, Obese. |
All inputs are validated and must stay within physiologically plausible ranges.
Frequently Asked Questions (FAQ)
Which method should I use?
The U.S. Navy method is recommended when you can measure neck, waist, and (for women) hips. Use the BMI estimate when you only know height, weight, and age.
How many times should I measure?
Take at least two measurements for each site and use the average. Measure at the end of a normal exhale and keep the tape level.
Do hydration and time of day matter?
Yes. Circumferences and scale weight vary throughout the day. Measure under consistent conditions, ideally in the morning.
Is this medical advice?
No. This tool is informational and not a substitute for professional medical advice or diagnosis.
What are healthy body fat ranges?
Ranges vary by sex, age, and goals. As a general guide, ACE categories: Men 6–24% (Athletic to Acceptable), Women 14–31%. Consult a professional for individualized targets.