General estimate for planning only — not medical advice. Consult a doctor about your specific situation.
Calculation details
Adult screening estimate only, not a diagnosis. Body composition, age, pregnancy, medical history, and population-specific risk can change interpretation; discuss health decisions with a qualified clinician.
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Use this result
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What does this calculator estimate?
For a 5-foot-10-inch man with a 34-inch waist and 15-inch neck, the U.S. Navy formula gives about 17.5 percent body fat: 86.010 x log10(34 - 15) - 70.041 x log10(70) + 36.76. Measurements are in inches.
- The U.S. Navy body-fat formula uses waist, neck, and height for men; women also use hip (U.S. Navy).
- The calculator estimates body fat; DEXA or hydrostatic weighing are the clinical gold standard.
- Body fat below about 5 percent for men is rarely sustained and can carry health risks.
How circumference methods work
Body fat percentage can be estimated from tape measurements using equations like the U.S. Navy method, which relates circumferences to body density. It's a practical approximation for tracking trends without expensive equipment.
Limitations to watch for
Estimate accuracy is ±3–5% vs DEXA or hydrostatic weighing. Measurement consistency matters — same tape position, same time of day. The method assumes typical body proportions; very athletic or atypical builds skew results.
How to use it in practice
Measure at the right spots (navel waist, neck below the larynx, widest hip) with a flexible tape, not compressing skin. Track monthly trends rather than single readings. Healthy ranges: ~8–20% men, ~18–30% women.
['Enter sex, height, and weight.', 'Enter the required circumference measurements.', 'Read the estimated body fat percentage.']
How this calculator works
Formula
Estimates body fat percentage from circumference measurements using the U.S. Navy method: for men, waist and neck at the navel; for women, waist, neck, and hip. Body density is estimated, then converted to fat %.
Worked example
Using the Navy method, a 180 lb man with a 30″ waist and 15″ neck estimates around 15–20% body fat depending on height and hip measurements.
Assumptions to verify
- Measurements are taken at the standard anatomical sites.
- The Navy equations apply to typical adult body types.
- The result is an estimate, not a clinical measurement.
Frequently asked questions
How is body fat estimated?
The U.S. Navy method uses waist, neck (and hip for women) circumferences plus height and weight in equations that estimate body density, then fat percentage.
How accurate is it?
Within about ±3–5% of lab methods like DEXA for most people — better for tracking trends than absolute numbers.
What measurements do I need?
Men: waist and neck. Women: waist, neck, and hip. Measure at the standard sites with a flexible tape.
What is a healthy body fat range?
Roughly 8–20% for men and 18–30% for women, varying with age and fitness goals.
Why is my scale's body fat different?
Scales use bioelectrical impedance, which is less accurate and varies with hydration — circumference methods can differ.
How do I reduce body fat?
Sustain a modest calorie deficit, strength training to preserve muscle, and protein intake — steady, measurable change.
Is this a medical measurement?
No — it's an estimate for tracking. Clinical assessment uses DEXA, hydrostatic weighing, or skinfold calipers by a professional.
Cite this tool
BoringToolsKit. “Body Fat Estimate Calculator.” boringtoolskit.com/body-fat-calculator/ (reviewed 2026-08-25). Free to reference in articles, syllabi, and answer posts with a link.
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How This Tool Works
Calculation Method
The tool applies the displayed formula or calculation logic to the values entered and returns a planning result.
Evidence basis
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Assumptions to Verify
- These tools provide general estimates for planning and education only.
- They are not medical advice and not a substitute for a qualified healthcare professional.
- Always consult your doctor or another healthcare provider about your specific situation.
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