Body Fat Calculator
All you need is a tape measure. This calculator uses the US Navy circumference method — usually within 3–4 percentage points of a DEXA scan, and much easier to repeat consistently.
How to use this calculator
- Measure in the morning, before eating, with relaxed muscles — the tape snug but not digging in.
- Men: neck just below the larynx, waist at the navel. Women: neck, waist at the narrowest point, hips at the widest.
- Take each measurement 2–3 times and average them, then enter the averages with your height and weight.
How the Navy method works
The US Navy circumference method (Hodgdon & Beckett, 1984) estimates body fat from the relationship between your height and key circumferences. In inches:
Men: %BF = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76Women: %BF = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387Validation studies against hydrostatic weighing show standard errors around 3–4% body fat — not perfect, but excellent for tracking change over time when you measure the same spots the same way.
What the numbers mean
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletic | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
Ranges per the American Council on Exercise; “essential fat” is the floor needed for basic physiology — it is not a target.
Frequently asked questions
How accurate is the tape method compared to DEXA?
Expect results within about 3–4 percentage points of a DEXA scan. The number itself may be slightly off, but if you measure the same spots each time, the trend is reliable.
Tips for consistent measurements?
Same time of day, same spots, tape level and snug without compressing skin, and average two or three readings. Consistency matters more than perfection.
How often should I remeasure?
Every 2–4 weeks. Body fat changes slower than scale weight, and measurement noise means daily readings would only confuse you.
Can I use this if I am very muscular or very overweight?
Extreme builds push circumference formulas further from the truth. Use it for trend tracking, and consider calipers or a DEXA scan for a one-off baseline.