Body Fat Percentage Calculator
A free body fat percentage calculator using the U.S. Navy circumference method — no calipers, scales, or scanners needed, just a tape measure. Works as a body fat calculator for men and a body fat calculator for women, with separate formulas and category ranges built in for each.
Reviewed for accuracy: January 2026 · Written and reviewed by Manzoor Ahmad, Pharmacist · Method sourced from the U.S. Naval Health Research Center (Hodgdon & Beckett, 1984)
Use Male for the body fat calculator for men formula (neck + waist), or Female for the body fat calculator for women formula (neck + waist + hip) — the U.S. Navy method uses a different equation for each because male and female fat distribution patterns differ.
Body Fat Percentage Chart by Category
These are the American Council on Exercise (ACE) reference categories — the most widely cited body fat percentage chart in fitness and clinical settings, separated by sex since men and women carry meaningfully different amounts of essential fat.
| Category | Men | Women |
|---|---|---|
| Essential fat | 2 – 5% | 10 – 13% |
| Athletic | 6 – 13% | 14 – 20% |
| Fitness | 14 – 17% | 21 – 24% |
| Acceptable / Average | 18 – 24% | 25 – 31% |
| Obese | 25% and above | 32% and above |
How This Body Fat Calculator Works
This is a body fat percentage calculator without calipers, scales, or scanners — it uses the U.S. Navy circumference method, developed by Hodgdon and Beckett at the Naval Health Research Center in 1984 and validated against underwater (hydrostatic) weighing, the gold-standard reference method of its era. All you need is a flexible tape measure.
Men (neck + waist)
BF% = 495 ÷ [1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)] − 450
Example: a man 5 ft 9 in (69 in) tall, with a 34 in waist and 15 in neck, works out to roughly 11% body fat.
Women (neck + waist + hip)
BF% = 495 ÷ [1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)] − 450
All measurements convert to inches internally before the formula runs — the constants above are calibrated specifically for inches.
How Accurate Is This Body Fat Calculator?
Circumference-based estimates are convenient, but they’re still estimates — here’s where this method holds up and where it doesn’t.
Typical margin of error
Validation studies against hydrostatic weighing put the standard error at roughly 3–4 percentage points either direction. That’s precise enough to track real changes over weeks and months, but not precise enough to treat a single reading as an exact number.
Least accurate at the lean end
The formula tends to overestimate body fat in very lean individuals — roughly below 15% for men and below 25% for women — and performs best in the mid-range. If you’re already quite lean, treat the number as a rough guide rather than gospel.
A thick or muscular neck skews results
Neck size is used as a stand-in for lean mass in the formula, so a naturally thick or heavily muscled neck can push the estimate lower than your true body fat. Compare it against our Lean Body Mass Calculator if that sounds like you.
Not a substitute for a BMI reading
Body fat percentage and BMI measure different things and can disagree — a muscular person can have a high BMI but low body fat, or vice versa. Run both on our BMI Calculator for the fuller picture.
Explore More Health Calculators
Body fat percentage is one piece of the picture. These related tools from our full health calculators library dig into weight, body shape, and clinical dosing measures.
Frequently Asked Questions
For men, the ACE “fitness” and “acceptable” categories span roughly 14–24%. For women, the equivalent range is about 21–31%. Athletes typically sit lower — 6–13% for men, 14–20% for women — while dropping below the essential-fat minimum (2–5% men, 10–13% women) is unsafe.
You need three measurements for men (height, neck, waist) or four for women (height, neck, waist, hip). Keep the tape horizontal and snug but not compressed, measure after a normal exhale, and avoid sucking in your stomach — see the “How and where to measure” panel above the calculator for exact placement.
Gym scales use bioelectrical impedance analysis (BIA), which estimates body fat from how electrical current moves through your body — a completely different method from the Navy tape method used here. Both are estimates, and hydration level alone can shift a BIA reading by several percentage points in either direction, so don’t expect the two numbers to match exactly.
Less so. The formula tends to overestimate body fat in lean individuals (roughly under 15% for men, under 25% for women), and a large neck circumference from muscle rather than fat can distort the result in either direction. Calipers or a DEXA scan are more reliable at the extremes.
Yes — body fat tends to rise gradually with age even at a stable body weight, largely because muscle mass declines over time. A body fat percentage that was “average” at 25 may sit in a different category by 55, which is one reason tracking your own trend over time matters more than comparing a single number to a chart.
BMI only uses height and weight, so it can’t tell muscle from fat. Body fat percentage measures composition directly through circumference, giving a clearer picture for athletes or anyone whose weight doesn’t tell the full story. Try our BMI Calculator alongside this one for a fuller view.
References
- Hodgdon, J.A. & Beckett, M.B. A Survey of Body Fat Content of U.S. Navy Male Personnel. Naval Health Research Center, 1984.
- Secretary of the Navy. OPNAVINST 6110.1L — Physical Readiness Program. December 29, 2025.
- American Council on Exercise (ACE). Percent Body Fat Norms for Men and Women. Referenced via ACEfitness.org.
- Centers for Disease Control and Prevention. About Body Mass Index (BMI). CDC.gov.