Body Fat Calculator

What this calculator does

This calculator estimates body fat percentage using the U.S. Navy method (circumference-based). You enter sex, height, weight (for context), and circumference measurements (waist, neck, and for females, hip). The result is a single body fat % value, often used alongside BMI for a rough picture of body composition.

It is useful for people who want a no-equipment estimate of body fat for general awareness or to track trends over time. Fitness enthusiasts and researchers sometimes use it as a simple proxy when calipers or DXA are not available. It is an estimate only; accuracy depends on measurement consistency and body shape.

How to use it

1. Select Unit (metric or imperial) and Sex (Male/Female).
2. Enter weight and height (used in the formula). For imperial, use Height (ft) and Height (in).
3. Measure waist at navel level, neck below the larynx, and for female, hip at the widest point. Enter circumferences in cm (this implementation uses cm for circumferences).
4. Read your estimated body fat % in the Result panel.

All inputs are in the "Inputs" section; the result updates as you change values. Consistency in measurement technique improves comparability over time.

Formulas used

U.S. Navy method

• Male:
  BF% = 495 / (1.0324 − 0.19077×log₁₀(waist − neck) + 0.15456×log₁₀(height)) − 450

• Female:
  BF% = 495 / (1.29579 − 0.35004×log₁₀(waist + hip − neck) + 0.22100×log₁₀(height)) − 450

All lengths in cm. The formula uses log base 10. Result is clamped to a plausible range (e.g. 3–50% male, 10–60% female) to avoid nonsensical values from measurement error.

The male equation uses waist and neck; the female equation adds hip circumference because of different fat distribution. Use the correct sex for the equation that applies to you.

Interpretation & examples

• Body fat % is only an estimate. Accuracy depends on measurement consistency (same time of day, same tape tension) and body shape. It can be off by several percentage points.
• General ranges (adults): essential fat ~2–5% (males), ~10–13% (females); fitness ~6–17% (m), ~14–24% (f); average and obese bands extend upward.
• Example 1: Male, 170 cm, waist 85 cm, neck 38 cm → result typically in the average range (mid-teens to low 20s % depending on exact values).
• Example 2: Female, 165 cm, waist 75 cm, neck 32 cm, hip 100 cm → result in a range that depends on the exact formula implementation; use for trend over time rather than absolute accuracy.

History & background

The U.S. Navy developed circumference-based equations for quick field assessment of body composition. They are still used in fitness and research as a simple, no-equipment proxy for body fat when calipers or DXA are not available. They are not as accurate as DXA or Bod Pod but are easy to replicate at home for tracking changes.

Limitations & safety notes

• Not medical or clinical advice. The Navy method can be off by several percentage points; it is sensitive to where you measure and how you hold the tape.
• It does not replace professional body composition testing (e.g. DXA, Bod Pod). Use for general awareness only, and consult a healthcare provider for health decisions or if you have conditions affected by body composition.
• Do not use this estimate as the sole basis for extreme dieting or body image decisions. For personalized advice, see a doctor or dietitian.