Body Fat Calculator (US Navy Method)
By Santaji GadepatilinUpdated October 27, 2026
The US Navy method estimates body fat percentage from simple tape measurements of the neck, waist and hips.
How to use the body fat calculator
Choose your sex, then enter your height, neck and waist measurements. Women also enter their hip measurement (men can ignore it). Measure in cm or inches.
The formulas (measurements in cm)
Men: %BF = 495 ÷ (1.0324 − 0.19077·log₁₀(waist − neck) + 0.15456·log₁₀(height)) − 450
Women: %BF = 495 ÷ (1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.22100·log₁₀(height)) − 450
Worked examples
- Man: height 178 cm, neck 38 cm, waist 85 cm → about 16.4%
- Woman: height 165 cm, neck 33 cm, waist 75 cm, hips 100 cm → about 29.4%
General body fat ranges
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| High | 25%+ | 32%+ |
Source: American Council on Exercise guidelines.
Body fat measurement methods compared
| Method | Typical accuracy | Cost and access |
|---|---|---|
| DEXA scan | ±1–2% | Clinic, expensive |
| Hydrostatic (underwater) weighing | ±2% | Labs, rare |
| Air displacement (Bod Pod) | ±2–3% | Some gyms and labs |
| Skinfold calipers (trained tester) | ±3–4% | Cheap |
| US Navy tape method | ±3–4% | Free — tape measure |
| Bioelectrical impedance (smart scales) | ±4–5% | Cheap, varies with hydration |
The Navy method is as good as most home options. Use the same method each time to track change.
Body fat by age (general guide)
Healthy body fat tends to rise slightly with age:
| Age | Men | Women |
|---|---|---|
| 20–39 | 8–19% | 21–32% |
| 40–59 | 11–21% | 23–33% |
| 60–79 | 13–24% | 24–35% |
Ranges follow commonly cited guidance based on BMI-matched data (Gallagher et al., 2000). They are a guide, not a diagnosis.
Essential fat
Some fat is vital for hormones, nerves and organs. Essential fat is about 2–5% for men and 10–13% for women. Going below these levels is dangerous, even for athletes.
Fat mass and lean mass
Multiply your weight by your body fat percentage to get fat mass. The rest is lean mass — muscle, bone, organs and water. Losing fat while keeping lean mass is the goal of most training plans.
Tips for consistent results
Measure in the morning before eating, take each measurement three times and use the average. Track the trend over weeks rather than any single reading.
This is an estimate, not a medical assessment.
Frequently asked questions
How accurate is the US Navy method?
It usually lands within about 3–4 percentage points of lab methods such as DEXA for most people. Accuracy depends heavily on measuring carefully.
Where exactly should I measure?
Neck just below the larynx; waist at the navel for men and at the narrowest point for women; hips at the widest point. Keep the tape level and snug, not tight.
What is a healthy body fat percentage?
Roughly 10–20% for men and 18–28% for women, depending on age and the source. Very low levels can be unhealthy too.
Why does my smart scale show a different number?
Smart scales use bioelectrical impedance, which changes with hydration, meals and exercise. Readings can vary by several percent from day to day.
How fast can I lower my body fat?
A realistic rate is about 0.5–1% of body fat per month with a modest calorie deficit and strength training.