bmicalculatorsystem.com
Enter a few measurements to estimate your body fat percentage, fat mass, and lean mass using the U.S. Navy method — instantly, and entirely in your browser.
Men & women · Free · Runs entirely in your browser
Measure with a snug, level tape: neck below the larynx, waist at the navel (men) or the narrowest point (women), and hips at the widest point. Results update instantly — nothing is stored or sent anywhere.
Your result
17.4
% body fat
You're in the fitness range — a healthy level of body fat.
Fat mass
13.1 kg
Lean (fat-free) mass
61.9 kg
Acceptable range
14 – 24%
Method
U.S. Navy
How it works
Two people at the same weight — even the same BMI — can carry very different amounts of fat. Body fat percentage measures the part that actually drives health risk, and the U.S. Navy circumference method estimates it from simple tape measurements, no calipers or scales required.
01
Neck and waist for men; women add the hips. A snug, level tape and your height are all the formula needs.
02
The Navy formula was validated against hydrostatic weighing and lands within a few points of a lab scan for most people.
03
Unlike BMI, it won't flag a muscular athlete as "overweight" — because it estimates fat, not just mass.
Classification
Healthy body fat differs between men and women — women carry more essential fat for hormonal and reproductive function. These ranges follow the American Council on Exercise.
Men
| Body fat | Category |
|---|---|
| 2 – 5% | Essential fat |
| 6 – 13% | Athletes |
| 14 – 17% | Fitness |
| 18 – 24% | Average |
| 25% and above | Obese |
Women
| Body fat | Category |
|---|---|
| 10 – 13% | Essential fat |
| 14 – 20% | Athletes |
| 21 – 24% | Fitness |
| 25 – 31% | Average |
| 32% and above | Obese |
The playbook
Body-fat percentage drops fastest when you lose fat and hold onto lean mass. These evidence-based habits do exactly that.
NUTRITION
A 300–500 kcal daily deficit drops fat at roughly 0.5 kg per week while sparing muscle. Aggressive cuts burn lean mass and stall your metabolism.
NUTRITION
Aim for 1.6–2.2 g of protein per kg of body weight while cutting. It protects muscle, blunts hunger, and keeps the weight you lose mostly fat.
TRAINING
Resistance training 2–4 times a week tells your body to retain muscle in a deficit, so your body-fat percentage falls from the top down — not the bottom up.
TRAINING
A few brisk walks or zone-2 sessions a week raise your energy burn without driving the appetite spike that long, grinding cardio often triggers.
RECOVERY
Under-sleeping raises cortisol and hunger hormones and shifts weight loss toward muscle instead of fat. Seven to nine hours is a fat-loss tool.
MINDSET
Body-fat estimates move slowly. Re-measure every 3–4 weeks, first thing in the morning, with the tape at the same spots — and judge the trend, not one reading.
Under the hood
The method fits body-fat percentage to log-transformed circumferences and height. Women's formula adds the hip measurement because fat distribution differs by sex. Fat mass is your weight times that percentage; lean mass is the rest.
Every result on this page is computed locally in your browser with these exact formulas. Nothing is uploaded, logged, or stored.
# U.S. Navy method (cm, base-10 logs)
# Men
BF% = 495 / (1.0324 − 0.19077·log10(waist − neck)
+ 0.15456·log10(height)) − 450
# Women
BF% = 495 / (1.29579 − 0.35004·log10(waist + hip − neck)
+ 0.22100·log10(height)) − 450
# Mass breakdown
fat_mass = weight × BF% / 100
lean_mass = weight − fat_massWhich to use
BMI and body fat percentage are complementary, not competing. BMI is the faster check — it needs only your height and weight and works well as a population-level screen. But it can't see the difference between muscle and fat, so it can misjudge athletes and very lean or very muscular people.
Body fat percentage targets the thing that actually matters for health: how much of your body is fat. The trade-off is that it depends on careful measurement and is an estimate, not a lab reading. For the clearest picture, check both — start with the main BMI calculator, then use this tool to see what's behind the number.
Checking a child instead? Body fat formulas for adults don't apply — use our children's BMI calculator, or read more in our health blog.
FAQ
This calculator uses the U.S. Navy circumference method, which estimates body fat from your height and tape measurements — neck and waist for men, plus hips for women. It is the same formula used by the U.S. Department of Defense and needs no calipers or scales, just a tape measure.
For most people it lands within about 3–4 percentage points of a DEXA or hydrostatic (underwater) scan — impressive for a method that needs only a tape measure. Accuracy drops at the extremes and depends heavily on measuring at the right spots, so treat the result as a solid estimate rather than a clinical reading.
It differs by sex. The American Council on Exercise considers roughly 14–24% acceptable for men and 21–31% for women. Athletes typically sit lower (6–13% men, 14–20% women), and essential fat — the minimum needed for basic function — is about 2–5% for men and 10–13% for women.
Use a snug, level, non-stretch tape. Measure your neck just below the larynx, your waist horizontally at the navel for men or at the narrowest point for women, and (women only) your hips at the widest point. Keep the tape parallel to the floor and don’t pull it tight enough to compress the skin.
They answer different questions. BMI relates weight to height and is a fast population-level screen, but it can’t tell muscle from fat. Body fat percentage targets the thing that actually matters for health — how much of you is fat — which makes it especially useful for athletes and very muscular people whom BMI often misclassifies. Using both together gives the clearest picture.
No. It is a screening estimate. A very high or very low result is a prompt to speak with a doctor or a registered dietitian, who can use clinical measurements and your full health history before drawing any conclusion.
The BMI calculator gives your category, healthy weight range, and BMI Prime in seconds.
Open the BMI calculator