Body Fat Calculator
Estimate your body fat percentage with the U.S. Navy tape-measure method. Enter a few circumference measurements to get your body fat percentage, category, and fat-versus-lean mass.
What body fat percentage tells you
Body fat percentage is the share of your total weight that is fat tissue, with the rest — muscle, bone, organs and water — making up your lean mass. Unlike a number on the scale, it describes composition: two people of the same weight and height can have very different amounts of fat. That’s why body fat percentage is often a more useful fitness indicator than BMI, which can’t tell muscle from fat and may flag a lean, muscular person as “overweight.”
What it can’t do is replace a medical assessment. Every at-home method gives an estimate with a margin of error, and the “healthy” ranges are broad guides rather than strict cut-offs. Some fat is essential — it cushions organs, stores energy and supports hormone function — so lower is not always better. Use the figure to understand your starting point and track change over time.
How to use this calculator
Measure your neck and waist (and hips for women) with a flexible tape, add your height, and the calculator estimates your body fat percentage and category. Enter your weight too and it also splits your total into fat mass and lean mass. For best results take each measurement two or three times and use the average, keeping the tape snug and level without compressing the skin.
How it’s calculated
This tool uses the U.S. Navy circumference method, which estimates body fat from the difference between your fat-storing and lean circumferences relative to your height. In words, it works from your waist minus neck measurement (plus hips for women) compared against your height: a larger waist relative to neck and height implies more fat. The underlying equations are logarithmic, so the calculator handles the maths — you just supply accurate tape measurements. Because it relies on where fat tends to gather, it’s reasonably good for average builds and less reliable at the extremes.
A worked example
Consider a man who is 180 cm tall with a 38 cm neck and a 90 cm waist. The method looks at his waist-minus-neck figure (52 cm) against his height and returns an estimate of roughly 18–19% body fat, which falls in the typical “fitness/average” range for men. If he also weighs 80 kg, that’s about 15 kg of fat mass and 65 kg of lean mass. Trimming the waist while keeping the neck stable would lower the estimate over time.
Estimation methods compared
| Method | How it works | Accuracy |
|---|---|---|
| DEXA scan | Low-dose X-ray, clinic-based | Gold standard; most precise |
| Hydrostatic weighing | Underwater displacement | Very accurate; lab only |
| Skinfold calipers | Pinch fat at several sites | Good with skilled tester |
| U.S. Navy tape method | Neck, waist (and hips) + height | Fair; great for tracking |
| BIA scales/handhelds | Tiny electrical current | Variable; sensitive to hydration |
Reference body fat ranges by sex
Women carry more essential fat than men for reproductive and hormonal reasons, so healthy ranges differ. These widely used American Council on Exercise–style bands are general guidance, not diagnostic thresholds:
| Category | Women | Men |
|---|---|---|
| Essential fat | 10–13% | 2–5% |
| Athletes | 14–20% | 6–13% |
| Fitness | 21–24% | 14–17% |
| Average / acceptable | 25–31% | 18–24% |
| Above range | 32%+ | 25%+ |
Limitations & tips
The Navy method assumes a fairly typical fat distribution, so it can misread very lean, very muscular or very heavy bodies, and small tape errors translate into noticeable swings in the result. BIA scales add their own quirk: readings shift with how hydrated you are, when you last ate or exercised, and even time of day. For consistency, measure first thing in the morning, before food and drink, in the same conditions each time. None of these tools diagnose health — body fat above the “average” band doesn’t automatically mean illness, nor does a low number guarantee fitness. If body composition matters for a health or athletic goal, consider a one-off DEXA scan for a baseline and discuss the results with a healthcare professional.
Frequently asked questions
How does the Navy body fat method work?
It estimates body fat from body circumferences — neck and waist for men, plus hips for women — together with height. It's free, needs only a tape measure, and is reasonably accurate for most people.
Where exactly do I measure?
Measure your neck just below the larynx, your waist at the navel for men or the narrowest point for women, and hips at the widest point for women. Keep the tape snug and level, and don't suck in.
Is it as accurate as a DEXA scan?
No. DEXA and hydrostatic weighing are more precise. The Navy method is a solid, repeatable estimate for tracking change — measure the same way each time and watch the trend rather than a single reading.
What is a healthy body fat percentage?
It depends on sex. Broadly, a “fitness” range is around 21–24% for women and 14–17% for men, with “average/acceptable” extending to roughly 31% and 24% respectively. Women naturally carry more essential fat than men. These are general guides, not targets everyone should hit, and athletes often sit lower.
Is body fat percentage better than BMI?
For judging fitness, often yes, because it distinguishes fat from muscle while BMI cannot. A muscular athlete can have a high BMI but low body fat. That said, BMI is quicker and needs no tape measure, so many people use both — BMI for a fast screen and body fat percentage for a closer look at composition.
Why do my scale and the tape method disagree?
They use different techniques with different error sources. Bioelectrical impedance scales pass a small current through the body and are heavily affected by hydration, recent meals and exercise, so they can read several points off and vary day to day. The tape method is more stable but assumes a typical fat distribution. Pick one method, use it consistently, and follow the trend.
Can body fat be too low?
Yes. Below the essential-fat level — roughly 10–13% for women and 2–5% for men — the body struggles to maintain hormones, temperature regulation and organ protection, and in women very low body fat can disrupt menstrual cycles. Extremely low body fat is not a health goal for most people. If you’re aiming for very low levels, do so under professional supervision.
Sources & references
- American Council on Exercise (ACE) — Body fat percentage averages in men and women — the typical/acceptable body-fat ranges used in this tool's reference table.
- Circumference-based predictions of body fat (PMC, National Institutes of Health) — the history and validation of the Hodgdon–Beckett "Navy" circumference method this calculator uses.
Last updated: July 2026 · How we calculate
BriskToolbox provides estimates for general information only and is not medical advice. Talk to a healthcare professional about your individual health.