Body Fat Calculator
Enter a few tape-measure circumferences and this calculator returns your estimated body fat percentage using the U.S. Navy method, a BMI-based cross-check, your fat mass and lean mass, the Jackson and Pollock ideal body fat for your age, and how much fat you would shed to reach it.
Formula
Worked example
A man 180 cm tall, 90 cm waist, 38 cm neck: 495 ÷ (1.0324 − 0.19077·log₁₀(52) + 0.15456·log₁₀(180)) − 450 ≈ 19.8% body fat. At 80 kg that is about 15.8 kg of fat and 64.2 kg of lean mass.
How the U.S. Navy Method Works
The U.S. Navy circumference method estimates body fat percentage from height, neck circumference, and waist circumference in men, with hip circumference added for women. These measurements feed into a logarithmic formula developed and validated by Hodgdon and Beckett in 1984 for the U.S. Navy as a practical alternative to underwater weighing. Because it relies on circumference rather than weight alone, it accounts for the fact that two people with identical BMI can have very different body compositions. The method has been shown to estimate body fat within roughly 3-4 percentage points of criterion measures for most adults when measurements are taken correctly.
How to Take Your Measurements
Use a flexible, non-stretch tape measure and keep it snug against the skin without compressing the tissue. Measure your neck just below the larynx (Adam's apple), sloping slightly downward toward the front. Measure your waist at the narrowest point, for men this is typically at the navel; for women it is the narrowest part of the torso, usually just above the navel. Women also measure the hip at its widest point, with feet together. Take each measurement twice and average the results to reduce error.
Healthy Body Fat Ranges by Sex
Healthy body fat ranges differ meaningfully between men and women because women require more essential fat for hormonal and reproductive function. The American Council on Exercise classifies essential fat as 10-13% for women and 2-5% for men, with the "fitness" range typically cited as 14-20% for women and 6-13% for men. Values above approximately 25% in men and 32% in women are generally associated with elevated cardiometabolic risk, though precise thresholds vary by age and the specific clinical guideline used. Age is relevant too, some fat accumulation with age is normal, so risk thresholds for older adults are sometimes adjusted upward.
Fat Mass, Lean Mass and the BMI Cross-check
If you also enter your weight, the calculator splits it into fat mass (your body fat percentage times your weight) and lean body mass (everything else, including muscle, bone, organs and water). Tracking lean mass alongside the percentage is useful when you are dieting, because the goal is usually to lose fat while keeping lean tissue. Adding your age unlocks a second, independent estimate from the BMI method, BFP equals 1.20 times BMI plus 0.23 times age minus 16.2 for men (minus 5.4 for women). The BMI method needs only height, weight and age, so when its result sits close to the Navy figure you can be more confident; a large gap usually means an unusual build, such as a very muscular frame that the BMI method reads as excess fat.
Your Ideal Body Fat and How Much to Lose
Healthy body fat is not a single number, it drifts upward with age, so the calculator reports the Jackson and Pollock ideal body fat for your age and sex. For example, a typical target is roughly 8.5% for a 20-year-old man and 17.7% for a 20-year-old woman, rising to about 20.9% and 26.3% by age 55. From your current estimate, weight and that age-based ideal, it works out the body fat (in pounds or kilograms) you would need to lose to reach the ideal, a concrete goal that is easier to act on than a bare percentage. Treat it as a guide rather than a prescription, since athletic performance, health history and personal goals all shift the right target.
Limitations of This Estimate
The U.S. Navy method is a screening tool, not a diagnostic test, and it carries meaningful uncertainty, results can differ by 3-5 percentage points from gold-standard methods such as dual-energy X-ray absorptiometry (DEXA) or air-displacement plethysmography. The BMI-method cross-check is rougher still, since BMI cannot tell muscle from fat. Accuracy is lower in people with very muscular builds (likely overestimating fat), in older adults with significant muscle loss, and in populations that differ from the military sample on which the formula was originally validated. Results should not be used to make medical decisions; consult a qualified healthcare provider if you are concerned about body composition or related health risks.
Body-fat categories (ACE)
| Category | Women | Men |
|---|---|---|
| Essential fat | 10-13% | 2-5% |
| Athletes | 14-20% | 6-13% |
| Fitness | 21-24% | 14-17% |
| Average | 25-31% | 18-24% |
| Above average | 32%+ | 25%+ |
American Council on Exercise body-fat ranges. Healthy ranges differ by sex and rise gently with age.
Frequently asked questions
Is the U.S. Navy body fat method accurate?
For most adults, the U.S. Navy method estimates body fat within about 3-4 percentage points of DEXA scan results when measurements are taken carefully. Accuracy decreases at the extremes of body composition, particularly for very muscular individuals, where the method tends to overestimate fat percentage. It is best understood as a reasonable screening estimate rather than a precise clinical measurement.
What is a healthy body fat percentage for women vs. men?
Healthy ranges are lower for men than for women because women carry more essential fat. Most clinical frameworks place healthy body fat at roughly 21-32% for adult women and 8-19% for adult men, though exact cutoffs vary by age and the source consulted. Values outside these ranges may warrant a conversation with a healthcare provider, particularly if accompanied by other metabolic risk factors.
Why do I need a hip measurement only as a woman?
The U.S. Navy formula uses different equations for men and women, and the female version includes hip circumference because women tend to store a greater proportion of fat in the hip and gluteal region. Including the hip measurement improves the accuracy of the estimate for women. The male formula omits the hip because it adds less predictive value in that population.
What is the difference between the Navy and BMI body fat methods?
The Navy method uses tape-measure circumferences (neck, waist and, for women, hips) with height, so it reflects where your body actually carries girth. The BMI method needs only height, weight and age and estimates body fat from BMI, which makes it quick but unable to distinguish muscle from fat. This calculator shows both: when they agree your estimate is more reliable, and a wide gap usually points to an unusually muscular or lean build.
How do I work out fat mass and lean body mass?
Fat mass is simply your body fat percentage multiplied by your weight, and lean body mass is your weight minus that fat mass, so it covers muscle, bone, organs and water. Enter your weight and the calculator reports both. When you are losing weight, watching lean mass hold steady while fat mass falls is a sign you are losing fat rather than muscle.