Body Fat Calculator
Estimate body fat percentage using the US Navy circumference method. Requires a flexible tape measure.
| Category | Male | Female |
|---|---|---|
| Essential Fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
For informational purposes only. Consult a healthcare professional.
For informational purposes only. Consult a healthcare professional for a clinical body composition assessment.
The US Navy Body Fat Formula
The US Navy body fat formula, also called the "circumference method," was developed by Hodgdon and Beckett in 1984 for the United States Navy to allow a simple, equipment-free estimate of body fat percentage. It uses two or three body measurements — height, neck, waist, and (for women) hip circumference — in a logarithmic formula that estimates body density, which is then converted to body fat percentage using the Siri equation.
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 measurements are in inches in the original formula (this calculator accepts centimetres and converts automatically). The formula is validated against hydrostatic weighing data and shows a standard error of estimate of approximately 3.5 percentage points.
How to Take Accurate Measurements
The accuracy of the formula depends heavily on correct measurement technique. Follow these guidelines:
- Waist: Stand relaxed with feet together. Measure around the abdomen at the level of the belly button (navel). The tape should be horizontal and parallel to the floor. Measure after a normal exhale. Do not hold your breath or pull in your stomach. Take three measurements and use the average.
- Neck: Stand straight and look forward. Place the tape just below the larynx (Adam's apple), angling slightly downward toward the front. For women, measure at the mid-neck. The tape should be snug but not compressing the tissue.
- Hip (women only): Stand with feet together. Measure around the widest part of your hips and buttocks. Keep the tape horizontal. This is usually 7–9 inches below the navel.
- Height: Measure without shoes, standing straight against a wall.
Body Fat Percentage Categories
| Category | Men | Women | Notes |
|---|---|---|---|
| Essential Fat | 2–5% | 10–13% | Minimum for physiological function. Below this level is dangerous. |
| Athletes | 6–13% | 14–20% | Competitive athletes, bodybuilders in off-season |
| Fitness | 14–17% | 21–24% | Fit and active, clearly defined muscle |
| Average | 18–24% | 25–31% | Typical range for healthy adults |
| Obese | 25%+ | 32%+ | Associated with elevated metabolic disease risk |
Women naturally carry more body fat than men due to hormonal differences and the fat stores needed to support pregnancy. This is normal and healthy. The "essential fat" level for women (10–13%) is significantly higher than for men (2–5%) for this reason.
Body Fat vs. BMI
BMI (Body Mass Index) is the most common screening tool for weight status, but it has a significant limitation: it cannot distinguish between fat mass and lean mass. A 100 kg professional rugby player and a 100 kg sedentary office worker of the same height have identical BMIs but completely different health profiles.
Body fat percentage measures what actually matters for metabolic health: the proportion of your body weight that is fat. Research consistently shows that body fat percentage is a stronger predictor of metabolic syndrome, type 2 diabetes, and cardiovascular disease risk than BMI alone.
Use both together for the most complete picture. Calculate your BMI with our BMI Calculator and compare it with your body fat percentage from this tool.
Frequently Asked Questions
How accurate is the US Navy body fat formula?
The US Navy circumference method typically has an error margin of ±3–4 percentage points compared to DEXA scanning, the gold standard. It is significantly more accurate than BMI for assessing body composition and is widely used in military fitness programs. Accuracy improves with careful, consistent measurement technique — measuring at the correct anatomical landmarks and taking multiple readings to average. The formula is less accurate for people who carry fat in atypical distributions.
Where exactly should I measure waist, neck, and hip?
Waist: measure at the level of the navel, not at the narrowest point. Keep the tape horizontal and measure after a normal exhale. Do not suck in your stomach. Neck: measure just below the larynx (Adam's apple), angling slightly downward. Hip (women only): measure at the widest point around the hips and buttocks. All measurements should be taken with a flexible tape measure pulled snug but not compressing the skin. Take 2–3 measurements and average them.
What is a healthy body fat percentage?
The American Council on Exercise (ACE) classifies body fat as: Essential fat (2–5% men, 10–13% women), Athletes (6–13% men, 14–20% women), Fitness (14–17% men, 21–24% women), Average (18–24% men, 25–31% women), and Obese (25%+ men, 32%+ women). "Essential fat" is the minimum required for physiological function — going below this level is dangerous. Most health organizations recommend staying in the "fitness" or "average" range for long-term health.
How is the US Navy formula different from the BMI formula?
BMI (Body Mass Index) uses only height and weight, making it blind to body composition. A muscular athlete and a sedentary person of the same height and weight get the same BMI but very different health profiles. The Navy formula directly measures body shape using circumferences, which correlates much better with actual fat distribution. It is possible to have a high BMI with low body fat (common in athletes) or a normal BMI with high body fat (known as "skinny fat" or TOFI — thin outside, fat inside).
What is the most accurate way to measure body fat?
DEXA (Dual-Energy X-ray Absorptiometry) scan is the gold standard, accurate to ±1–2%, but requires a medical facility. Hydrostatic (underwater) weighing is also very accurate at ±1–3%. Air displacement plethysmography (Bod Pod) is similar in accuracy. Bioelectrical impedance (home scales, handheld devices) is fast but can vary by ±5–8% based on hydration. Skinfold calipers with an experienced technician give ±3–5% accuracy. The US Navy formula (used here) gives ±3–4% and is free, requiring only a tape measure.
Related Calculators
- BMI Calculator — Body Mass Index with WHO weight categories
- Ideal Weight Calculator — Four formula comparison (Devine, Robinson, Miller, Hamwi)
- Calorie Calculator — Daily calorie needs based on your size and activity level