Body Fat Calculator

Estimate your body fat percentage from neck, waist (and hip for women) using the US Navy circumference method. Get fat mass, lean body mass, and ACE/ACSM healthy ranges.

Kalkuleta hii bado haijatafsiriwa kwa Kiswahili.

Tunaonyesha toleo la Kiingereza wakati tunafanya kazi ya tafsiri.

How to measure

Neck: just below the larynx (Adam's apple), tape level, not pulled tight.Waist: at the narrowest point (usually at the navel), at the end of a normal exhale.

Age

Weight (lb)

Height (in)

Neck (in)

Waist (in)

I don't have a tape measure

Uses the Deurenberg estimate (weight, height, age, sex only). Less accurate (±4%) than the US Navy method with measurements (±3%).

Body fat percentage

16.8%— Fitness

US Navy method

Fat mass

25.8 lb

Lean body mass

128.2 lb

Body Fat Scale

0%5%14%18%25%50%

You are within or below the healthy range for your age.

Healthy ranges by age (ACSM)

Age	Men	Women
18–29	11–17%	16–22%
30–39	13–19%	17–23%
40–49	16–21%	19–24%
50–59	17–22%	22–27%
60+	18–23%	22–28%

Adapted from ACSM's Health-Related Physical Fitness Assessment Manual, 5th ed. (2013), 50–80th percentile range.

You are in the fitness range — a healthy result for most adults who exercise regularly.

Compare with other tools

BMI Calculator

See whether this number matches what your weight-and-height BMI says.

Open BMI

BMR Calculator

Use your body fat percentage to get a more accurate calorie target via Katch-McArdle.

Open BMR

Sleep Calculator

Optimise recovery — sleep cycles affect both fat loss and muscle retention.

Open Sleep

Imesasishwa: 19 Julai 2026

Body fat calculator. US Navy method for body fat percentage.

A body fat calculator estimates your body fat percentage from neck, waist, and hip measurements using the US Navy circumference method. It also returns your fat mass and lean body mass in a single step, without a scan or lab visit.

What Is Body Fat Percentage?

Body fat percentage is the share of your total body weight that is made up of fat tissue, with the remainder being muscle, bone, organs, water, and connective tissue. A 180 lb (82 kg) man with 20% body fat is carrying about 36 lb (16.4 kg) of fat and roughly 144 lb (65.6 kg) of lean body mass. Unlike weight alone, this number directly answers the question "how much of me is actually fat?" — compare with your BMI to see why the two metrics often disagree.

BMI and body fat percentage answer fundamentally different questions. BMI asks "is my weight high relative to my height?" and it is calculated as a simple ratio. Body fat percentage asks "what fraction of my body is actually fat tissue?" and it requires body-shape data. A 5'7" (170 cm), 161 lb (73 kg) strength-trained man with a 41 cm (16 in) neck and an 82 cm (32 in) waist has a BMI of 25.3 — technically "overweight" by WHO standards — but the US Navy formula puts his body fat near 13%, well inside the athletic range. For muscular people, gym-goers, and anyone who lifts regularly, body fat percentage is the far more honest health number.

This calculator uses the US Navy circumference method developed in 1984 by Dr. James Hodgdon and Dr. Maureen Beckett at the Naval Health Research Center. It needs only a flexible tape measure, has an average error of ±3–4% compared to a DEXA scan, and is the official body composition assessment method used by the US Department of Defense for military fitness standards. That combination — low cost, no equipment beyond a tape, and real scientific validation — is why it is the dominant formula on Calculator.net, Omnicalculator, and most serious fitness sites.

How to Use the Body Fat Calculator

The calculator turns a few tape measurements into a full body-composition readout — body fat percentage, fat mass, lean body mass, an ACE category badge, and how far you are from the healthy range for your age. Pick your unit system and the tool converts everything for you.

1. Choose your unit system (metric: kg and cm, or imperial: lb and inches) and your sex — the female formula adds a hip measurement.

2. Enter your age, height, and weight. Weigh yourself first thing in the morning, after using the bathroom and before eating or drinking.

3. Measure your neck: place the tape just below the larynx (Adam's apple), look straight ahead, and keep the tape level and snug but not tight.

4. Measure your waist: at the level of the navel for men, at the narrowest point for women. Read it at the end of a normal exhale — do not suck in your stomach.

5. Women only — measure your hip circumference around the widest part of the buttocks, feet together and the tape parallel to the floor.

6. Read your results. The calculator shows your body fat percentage, the ACE category, your fat mass and lean body mass, and the amount of fat to lose to reach the healthy range for your age and sex.

For example, a 30-year-old man at 180 cm and 80 kg who measures a 40 cm neck and a 90 cm waist reads 18.4% body fat — about 14.7 kg of fat and 65.3 kg of lean mass — landing in the ACE "average" band and inside the healthy range for men aged 30–39. No tape measure handy? Switch to the secondary Deurenberg method, which estimates body fat from BMI, age, and sex alone. It is less accurate (standard error near ±4%) and tends to overstate body fat in muscular people, so use the US Navy method whenever you can.

US Navy Body Fat Formula

BFP_{male} = \frac{495}{1.0324 - 0.19077 \cdot \log_{10}(W - N) + 0.15456 \cdot \log_{10}(H)} - 450

$BFP$ = Body fat percentage (%)
$W$ = Waist circumference (cm)
$N$ = Neck circumference (cm)
$Hp$ = Hip circumference, women only (cm)
$H$ = Height (cm)

The formula above is the US Navy male equation (Hodgdon & Beckett, 1984), a logarithmic regression model calibrated on body composition data collected at the Naval Health Research Center. It was derived so that trained personnel could estimate body fat with a tape measure instead of a hydrostatic weighing tank.

For women the formula adds hip circumference as a third measurement, because female fat distribution is concentrated around the hips and thighs rather than the abdomen:

BFP_{female} = \frac{495}{1.29579 - 0.35004 \cdot \log_{10}(W + Hp - N) + 0.22100 \cdot \log_{10}(H)} - 450

Worked example — a 30-year-old man, height 170 cm, weight 70 kg, waist 85 cm, neck 38 cm:

\log_{10}(85 - 38) = \log_{10}(47) \approx 1.6721

\log_{10}(170) \approx 2.2304

BFP = \frac{495}{1.0324 - 0.19077 \cdot 1.6721 + 0.15456 \cdot 2.2304} - 450

BFP = \frac{495}{1.0324 - 0.3189 + 0.3448} - 450 \approx 17.8\%

Fat mass and lean body mass follow directly:

Fat mass = 70 × 17.8/100 ≈ 12.5 kg (about 27.5 lb)
Lean body mass = 70 − 12.5 = 57.5 kg (about 126.8 lb)

Secondary method — Deurenberg BMI-based formula (fallback when no tape measure is available):

BFP = 1.20 \cdot BMI + 0.23 \cdot Age - 10.8 \cdot S - 5.4

where Age is in years and S = 1 for men, S = 0 for women. This formula was published by Paul Deurenberg and colleagues in the *British Journal of Nutrition* in 1991 and has a standard error of about ±4.1%. It inflates body fat in muscular adults because it inherits all the limitations of BMI, so it should only be used when circumference measurements are not possible.

Body Fat Percentage Categories (ACE)

Category	Men	Women
Essential fat	2–5%	10–13%
Athletes	6–13%	14–20%
Fitness	14–17%	21–24%
Average (acceptable)	18–24%	25–31%
Obese	25% and above	32% and above

Real-World Body Fat Calculation Examples

Example 1 — 30-Year-Old Man in the Average Range

David is 30, stands 180 cm (5'11"), weighs 80 kg (176 lb), with a 40 cm neck and a 90 cm waist. US Navy male formula: log₁₀(90 − 40) = log₁₀(50) ≈ 1.6990; log₁₀(180) ≈ 2.2553. BFP = 495 / (1.0324 − 0.19077·1.6990 + 0.15456·2.2553) − 450 ≈ 18.4%. That works out to 14.7 kg (32.4 lb) of fat mass and 65.3 kg (144 lb) of lean body mass. On the ACE scale, 18.4% sits in the "average" band for men (18–24%), and it is already inside the healthy range the calculator shows for a man aged 30–39 (13–19%). Losing roughly 1.5 kg of fat while protecting his lean mass would bring him to about 17% — the top of the "fitness" band.

Example 2 — 30-Year-Old Woman, Hip Measurement Included

Elena is 30, 165 cm (5'5"), 65 kg (143 lb), with a 32 cm neck, a 75 cm waist, and 95 cm hips. US Navy female formula: log₁₀(75 + 95 − 32) = log₁₀(138) ≈ 2.1399; log₁₀(165) ≈ 2.2175. BFP = 495 / (1.29579 − 0.35004·2.1399 + 0.22100·2.2175) − 450 ≈ 27.4%. That is 17.8 kg (39.2 lb) of fat mass and 47.2 kg (104 lb) of lean body mass. The ACE badge reads "average" for women (25–31%), but 27.4% is above the age-specific healthy band the tool uses for women 30–39 (17–23%), so the calculator flags roughly 2.9 kg of fat to lose to reach the top of that range — a realistic 6–9 month goal, not a crash diet.

Example 3 — Muscular Lifter and the BMI Paradox

Marcus is 32, 170 cm (5'7"), 73 kg (161 lb), with a 41 cm neck and an 82 cm waist. His BMI is 73 / 1.70² = 25.3, which the WHO labels "overweight." But the US Navy formula tells a different story: log₁₀(82 − 41) = log₁₀(41) ≈ 1.6128; log₁₀(170) ≈ 2.2304. BFP = 495 / (1.0324 − 0.19077·1.6128 + 0.15456·2.2304) − 450 ≈ 12.9%. That is only 9.4 kg (20.7 lb) of fat and 63.6 kg (140 lb) of lean mass, placing him in the ACE "athletes" band (6–13%) rather than "overweight." This is the textbook case where BMI and body fat disagree: the scale calls him overweight, his composition is athletic. It is exactly why lifters distrust BMI — compare the two readings side by side.

Limitations of the US Navy Body Fat Estimate

The US Navy method is a circumference-based estimate, not a body scan. It applies a population regression to your neck, waist, hip, and height, so it predicts body fat from your body shape rather than measuring fat tissue directly. Its average error is about ±3–4% versus a DEXA scan — good enough to track your own trend over time, but not a clinical-grade number. Treat a reading of 18% as "somewhere around 15–21%," not an exact figure.

Because it was calibrated on 1980s US military personnel, the formula fits people near that build best and drifts for outliers: very lean bodybuilders, people with very high body fat, older adults who have lost muscle, and pregnant women can all get readings that are off by more than the typical margin. Measurement error and daily fluctuations matter too — a full bladder, water retention, a recent meal, or 1 cm of tape movement can shift the result by 1–2 percentage points.

The method also cannot tell you where your fat sits. It does not distinguish visceral (abdominal) fat from subcutaneous fat, and it does not replace a waist-circumference risk check — a waist over 40 inches (102 cm) for men or 35 inches (88 cm) for women signals elevated metabolic risk on its own. Remember, too, that essential fat — the biological floor of 2–5% for men and 10–13% for women — is required for hormones, organ protection, and immune function; "lower is always better" is false.

Finally, body fat percentage is a wellness estimate, not a medical diagnosis. The ACE category is a general reference, while the healthy range the tool shows is age- and sex-specific (based on ACSM percentiles). Use the result as one input alongside waist size, blood pressure, blood glucose, and overall fitness — and discuss any health decision with a qualified professional rather than acting on a single number.

Common Body Fat Measurement Mistakes

Measuring the waist at the wrong spot. Measure at the level of the navel for men and at the narrowest point of the torso for women — not at the belt line or over the hip bones. Take the reading at the end of a normal exhale, and never suck in your stomach; that alone can drop the estimate by several points.
Treating the tape estimate like a DEXA scan. The US Navy method carries a ±3–4% error against DEXA. Use it to follow your own trend, not as an exact clinical value, and do not panic over a single half-percent change between two mornings.
Confusing body fat percentage with BMI. BMI only compares weight to height and cannot separate muscle from fat, while body fat percentage measures how much of you is actually fat. A muscular lifter can be "overweight" on BMI and "athletic" on body fat at the same time — the two metrics answer different questions.
Using the Deurenberg (BMI-based) method for athletes. The BMI-based fallback inherits all of BMI's flaws and overstates body fat in muscular people. Whenever you have a tape measure, use the US Navy circumference method instead — it reads body shape, which is what actually drives the estimate.
Pulling the tape too tight or too loose. Keep the tape flat against the skin, level, and snug without compressing the tissue. Both over-tightening and leaving slack introduce error, and a 1 cm difference in waist or neck can shift the result by 1–2 percentage points.
Measuring at inconsistent times. Body fat moves slowly, so bloating, water retention, and post-meal readings create noise that swamps real change. Always measure in the morning, fasted, under the same conditions, and take each site three times to average out mistakes.
Fixating on the scale instead of the tape. Losing weight and losing fat are not the same. During strength training your scale weight can stay flat — or rise — while your body fat percentage falls and your clothes fit better, so track waist, neck, and body fat every four weeks alongside your weight.

Body Fat Calculator — Frequently Asked Questions

How accurate is the US Navy body fat calculator?

The US Navy circumference method has a mean error of about ±3–4% compared with a DEXA scan. Studies of military personnel have found it tends to slightly underestimate lean men and overestimate women, but for a home tool that needs only a tape measure it is the best accuracy available outside a clinical lab — and it is the method the US Department of Defense uses for its body-composition standards.

What is the difference between BMI and body fat percentage?

BMI is just weight divided by height squared; it cannot tell muscle and fat apart. Body fat percentage directly estimates how much of your body is fat tissue. A 5'7" muscular man with a BMI of 25.3 ("overweight") can have only about 13% body fat — which is athletic. For different interpretation thresholds see our BMI Calculator.

What is a healthy body fat percentage for men and women?

According to the American Council on Exercise (ACE), healthy ranges for men are: essential 2–5%, athletes 6–13%, fitness 14–17%, average 18–24%, obese 25%+. Women naturally carry more: essential 10–13%, athletes 14–20%, fitness 21–24%, average 25–31%, obese 32%+. The healthy band also shifts with age — ACSM lists 16–21% for men aged 40–49 and 19–24% for women of the same age.

Can I use my body fat percentage to get a more accurate calorie need?

Yes. Once you know your body fat percentage, you can use the Katch-McArdle formula, which bases BMR on lean body mass instead of total weight. It is more accurate than Mifflin-St Jeor or Harris-Benedict for lean or muscular people. Plug your result into our BMR Calculator (Katch-McArdle method) to get a personalized calorie target. If you do not know your body fat percentage yet, measure it here first.

Why are the formulas different for men and women?

Women biologically carry more body fat than men — essential fat alone is 10–13% for women versus 2–5% for men — because female fat supports reproductive and hormonal function. Male fat concentrates around the abdomen, while female fat also accumulates on the hips and thighs. The US Navy female formula adds hip circumference as a third measurement to capture that distribution; the male formula uses only neck and waist.

How do I lower my body fat percentage?

Prioritize strength training three to four times per week with compound lifts (squat, deadlift, press, row), which protects lean mass while you lose fat. Hit 0.7–1.0 grams of protein per pound of body weight daily, run a moderate 300–500 calorie deficit rather than a crash diet, and protect 7–9 hours of sleep, since sleep debt raises cortisol and stores fat around the waist — our Sleep Calculator can plan your sleep windows. Recheck every four weeks to confirm the fat, not the muscle, is coming off.

How fast can I safely lose body fat?

A safe rate is about 0.5–1% body fat per month, or roughly 3–5% over six months. Faster loss usually costs muscle. Never drop below essential fat — 5% for men, 13% for women — which the body needs for hormones, organs, and immune function.

How often should I remeasure my body fat?

Remeasure every four weeks, in the morning, fasted, before eating or drinking. Body fat changes slowly, so weekly checks mostly show noise. Your scale weight can stay flat while your body fat drops — the tape catches what the scale misses.

Is this body fat calculator free? Do I need to sign up?

Yes, this body fat calculator is completely free, with no sign-up, no registration, and no email required. All measurements are processed locally in your browser — nothing is sent to a server — so your personal data stays on your device. You can use the tool as many times as you want.

What other methods exist for measuring body fat percentage?

DEXA scans are the clinical gold standard (error ±1–2%) but cost $100–300 per session and require a radiology center. Hydrostatic (underwater) weighing is a lab procedure. Skinfold calipers, in trained hands, are accurate to ±3–5%. Bioelectrical impedance (BIA) scales vary by ±5–8% because they depend heavily on hydration. The US Navy tape method offers the best at-home balance: only a tape measure needed and ±3–4% accuracy.

Why are my neck and waist used — not just weight and height?

Circumference measurements capture actual body shape in a way that weight and height cannot. Two people who weigh exactly 180 lb at 5'10" can have very different waist-to-neck ratios, and therefore very different body fat percentages. The US Navy formula exploits this shape information: a bigger waist relative to the neck implies more abdominal fat, which drives the estimate up. That is why the method works without a laboratory scan.

Is body fat percentage a medical diagnosis?

No. This is a wellness estimate, not a medical assessment. The US Navy method carries a ±3–4% error, cannot see visceral fat or where fat sits, and was calibrated on a specific population. Use it alongside your waist measurement, blood pressure, and overall fitness, and consult a healthcare professional before making any health decision based on the result.

Vyanzo na Marejeo

Maudhui yamethibitishwa na Timu ya Smart Calculators