Body Fat Calculator
Estimate your body fat percentage with the U.S. Navy tape-measure method — no scale or scan needed, just a soft measuring tape.
Enter your weight below for fat/lean mass estimates: wt
How to measure
Use a soft tape, relaxed and level, not compressing the skin. Neck: just below the larynx. Waist: at the navel for men, at the narrowest point for women. Hips (women): at the widest point. Measure on bare skin, exhale normally, and take the average of two readings.
Women: 495 ÷ (1.29579 − 0.35004·log₁₀(waist+hip−neck) + 0.22100·log₁₀(height)) − 450
Height 178 cm, neck 38 cm, waist 85 cm. Waist − neck = 85 − 38 = 47.
495 ÷ (1.0324 − 0.19077 × log₁₀(47) + 0.15456 × log₁₀(178)) − 450 = 495 ÷ (1.0324 − 0.19077 × 1.6721 + 0.15456 × 2.2504) − 450 = 495 ÷ 1.0614 − 450 ≈ 16.4% — the "Fitness" category (14–17% for men).
Height 165 cm, neck 32 cm, waist 75 cm, hip 98 cm. Waist + hip − neck = 75 + 98 − 32 = 141.
495 ÷ (1.29579 − 0.35004 × log₁₀(141) + 0.22100 × log₁₀(165)) − 450 = 495 ÷ (1.29579 − 0.35004 × 2.1492 + 0.22100 × 2.2175) − 450 = 495 ÷ 1.0340 − 450 ≈ 28.7% — the "Average" category (25–31% for women).
The extra hip term for women is what makes the female formula structurally different from the male one, not just a different set of constants — it reflects that fat distribution patterns differ enough by sex that waist and neck alone don't estimate as reliably for women.
Body fat categories
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
Body fat percentage tells you something BMI can't — how much of your weight is fat versus muscle. It's the better metric for tracking a recomposition (losing fat while keeping or building muscle), where the scale can barely move while your body changes. Use consistent technique and compare trends, not single readings. Pair with the lean body mass and BMI calculators for a fuller picture.
How body fat methods compare
| Method | Typical accuracy vs. DEXA | Notes |
|---|---|---|
| U.S. Navy tape (this calculator) | ±3–4 points | Free, needs only a tape measure |
| Bioelectrical impedance (home scale) | ±3–8 points | Sensitive to hydration and meal timing |
| Skinfold calipers | ±3–5 points | Needs a trained, consistent technician |
| DEXA scan | Reference standard | Clinical/lab equipment required |
| Hydrostatic (underwater) weighing | Reference standard | Requires a specialized facility |
No field method matches a lab scan exactly, but the tape method's error is consistent enough in one direction for a given body type that it's genuinely useful for tracking change over weeks and months, even if the single-point number carries a few points of uncertainty.
Common body fat measurement mistakes
- Measuring the waist at the wrong landmark for your sex. Men measure at the navel; women measure at the narrowest point — mixing these up shifts the result noticeably.
- Comparing readings taken at different times of day. Food, fluid, and bloating can shift the waist measurement by up to an inch; measure at a consistent time for comparable trend data.
- Expecting an accurate number for a very muscular build. Because the formula relies only on circumference, it can overestimate body fat for people with a thick, muscular neck or waist relative to their actual leanness.
Frequently asked questions
How does the Navy method work?
It estimates body fat from neck, waist (and hip for women) tape measurements plus height.
What is a healthy body fat percentage?
Men ~10–20% fit; women ~18–28%. Women carry more essential fat.
How accurate is it?
Usually within 3–4 points of DEXA; best for tracking change with consistent technique.
Does it work well for very muscular people?
Not as well — since it relies only on circumference, it tends to overestimate body fat for a very muscular build with a thicker neck or waist relative to actual leanness.
Does time of day affect the waist measurement?
Yes, by up to an inch depending on food, fluids, and bloating — measure at a consistent time of day for comparable results over time.
Related calculators
Medical disclaimer: A tape-based estimate, not a clinical measurement. Not medical advice. For precise body composition, consider DEXA or hydrostatic testing. Formula: U.S. Navy circumference method. Last reviewed: September 2026.