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.

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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

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

This free 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.

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 30-inch (75 cm) waist has a BMI of 25.3 — technically "overweight" by WHO standards — but the US Navy formula puts his body fat at roughly 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 Measure and Calculate Body Fat Percentage

To measure body fat percentage with the US Navy method you need only a flexible (cloth or vinyl) tape measure and the information below. The method is trustworthy because it works with real body-shape data — neck and waist circumferences — rather than just weight and height like BMI does.

Step-by-step measurement process:

1. Record your height in inches without shoes, standing tall against a wall.

2. Weigh yourself in pounds first thing in the morning, after using the bathroom and before eating or drinking.

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

4. Measure your waist circumference: at the level of the navel for men, at the narrowest point for women. Take the reading 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, with feet together and tape parallel to the floor.

6. Enter your sex, age, height, weight, and all circumferences into the calculator above. The result updates instantly, and you will see your body fat percentage, fat mass, lean body mass, and category.

Worked example — a 30-year-old man, 5'8" (172 cm), 176 lb (80 kg), neck 15.5 in (39 cm), waist 34 in (87 cm): the US Navy male formula returns about 19.8% body fat. That means roughly 35 lb (15.8 kg) of fat mass and 141 lb (64.2 kg) of lean body mass. On the ACE scale, 19.8% sits in the middle of the "average" range for men (18–24%), with the "fitness" category starting at 17% and below.

If you do not have a tape measure, the calculator also offers a secondary Deurenberg method that uses only BMI, age, and sex. It is less accurate (standard error ±4.1%) 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% (R² = 0.79). 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.

Real-World Body Fat Calculation Examples

Example 1 — 28-Year-Old Male Office Worker

Mark is 5'9" (175 cm), weighs 172 lb (78 kg), neck 15.75 in (40 cm), waist 36.25 in (92 cm). US Navy formula: log₁₀(92 − 40) = log₁₀(52) ≈ 1.7160; log₁₀(175) ≈ 2.2430. BFP = 495 / (1.0324 − 0.19077·1.7160 + 0.15456·2.2430) − 450 ≈ 22.4%. His fat mass is 78 × 22.4/100 ≈ 17.5 kg (38.5 lb); lean body mass ≈ 60.5 kg (133.5 lb). On the ACE scale, 22.4% sits squarely in the "average" band for men (18–24%). To reach the "fitness" category (14–17%) Mark would need to drop roughly 10–13 lb (4.5–6 kg) of fat while keeping his lean mass, which realistically takes 4–6 months of structured training and moderate calorie deficit.

Example 2 — 32-Year-Old Muscular Lifter (BMI vs Body Fat Paradox)

Dave is 5'7" (170 cm), weighs 161 lb (73 kg), neck 16.25 in (41 cm), waist 29.5 in (75 cm). His BMI = 73 / 1.70² = 25.3, which the WHO classifies as "overweight". But the US Navy formula returns about 13% body fat — below the ACE "fitness" cut-off (14–17%) and on the edge of the athletic range (6–13%). His fat mass is only 9.5 kg (21 lb) and lean body mass is 63.5 kg (140 lb). This is the textbook BMI failure case: the scale and the BMI chart label Dave "overweight", but his body composition is genuinely athletic. Body fat percentage is the only metric that tells the truth here, and this is exactly why strength-training communities treat BMI as unreliable for lifters.

Example 3 — 40-Year-Old Woman After Three Children

Lisa is 5'2" (158 cm), weighs 143 lb (65 kg), neck 13 in (33 cm), waist 34 in (86 cm), hip 39.5 in (100 cm). US Navy female formula: log₁₀(86 + 100 − 33) = log₁₀(153) ≈ 2.1847; log₁₀(158) ≈ 2.1987. BFP ≈ 33.8%. Fat mass ≈ 22.0 kg (48.5 lb); lean body mass ≈ 43.0 kg (94.8 lb). According to the ACSM 40–49 age range, healthy body fat for women is 19–24%, and the ACE "obese" threshold starts at 32%. Lisa is just above that line. A realistic goal is losing about 13–15 lb (6–7 kg) of fat over 6–9 months through strength training, 0.8–1.0 g of protein per pound of body weight, and a modest 300–500 calorie daily deficit — not a crash diet.

Practical Tips to Improve Your Body Fat Percentage

Measure consistently: every morning, fasted, right after waking up, wearing minimal clothing. Place the tape snug against the skin without compressing it, breathe normally, and record the same three sites. Consistent technique lets you detect the small changes (0.5% body fat per month) that the bathroom scale will completely miss.
Stop fixating on the scale. Losing weight and losing fat are not the same thing. If you are strength training, your scale weight may stay flat — or even rise — while your body fat percentage drops and your clothes fit better. Measure waist, neck, and body fat every 4 weeks alongside your weight for the real picture.
Prioritize strength training over cardio-only plans. Cardio alone (running, walking, cycling) reduces total weight but also burns muscle, which keeps your body fat percentage stubbornly high. Lift weights 3–4 times per week using compound movements (squat, deadlift, press, row). Muscle is what gives you the lean body mass the scale cannot see.
Hit your protein target. Research supports 0.7–1.0 grams of protein per pound of body weight per day (1.6–2.2 g/kg) during fat loss. Good sources: chicken, turkey, eggs, Greek yogurt, cottage cheese, lean beef, fish, whey protein, tofu, and legumes. Adequate protein protects muscle while you are in a calorie deficit.
Be patient — a healthy rate is 0.5–1% body fat per month. Trying to drop 5% body fat in a single month is unrealistic and will cost you muscle mass. A sustainable goal is 3–5% body fat over 6 months, with progress logged every 4 weeks. Slower losses stick; crash diets rebound.
Never go below essential fat levels: 5% for men and 13% for women is the biological floor. Below those cut-offs you risk hormonal dysfunction, loss of bone density, immune suppression, and (for women) loss of menstrual cycle. "Lower is better" is false — body fat below 10% for men and 18% for women is only sustainable short-term for competitive bodybuilders.
Protect recovery and sleep. Deep sleep is when growth hormone spikes, muscle repairs, and fat oxidation peaks. Chronic sleep debt raises cortisol, which preferentially stores fat around the waist and undermines every workout you do. Aim for 7–9 hours per night — our Sleep Calculator can plan sleep windows around your wake time.

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 ±3–4% compared to a DEXA scan. The US Marine Corps Body Composition Survey (Friedl et al., 2022) found the formula underestimates men by about 2.5–2.6% and overestimates women by 1.3–2.3% on average. For a home tool that costs nothing beyond a tape measure, this is the best accuracy currently available outside a clinical lab, and it is the method officially used by the US Department of Defense.

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 measures how much of your body is fat tissue. A 5'7" muscular man with a BMI of 25.3 ("overweight") can have only 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 ranges shift slightly with age — ACSM lists 16–21% as healthy 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 significantly 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 distribution 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 accurately; the male formula uses only neck and waist.

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 are only available at radiology centers. 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.

How do I avoid measurement mistakes with the tape?

The most common errors are: pulling the tape too tight or leaving it too loose, sucking in the stomach while measuring the waist, measuring during bloating or water retention, and taking measurements at different times of day. Always measure in the morning, fasted, after a normal exhale, with the tape flat against the skin but not compressing it. Take each measurement three times and use the average. A 1 cm difference can shift your result by 1–2% body fat.

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 neck implies more abdominal fat, which drives the body fat estimate up. This is why the method works without needing a laboratory scan.

Key Terms

Body Fat Percentage (BFP)

The share of your total body weight that is fat tissue. Example: a 180 lb person at 20% body fat is carrying 36 lb of fat and 144 lb of lean mass.

Lean Body Mass (LBM)

Everything in your body that is not fat: muscle, bone, organs, water, and connective tissue. Formula: LBM = total weight − fat mass. Used in the Katch-McArdle BMR equation.

Fat Mass

The total weight of fat tissue in the body, expressed in pounds or kilograms. Includes both essential fat (around organs) and storage fat (under the skin and around the abdomen).

US Navy Method

A logarithmic regression formula developed by Hodgdon and Beckett in 1984 that estimates body fat from neck, waist, hip (women only), and height. The official body composition test for the US Department of Defense.

Essential Fat

The minimum body fat required for normal physiological function: 2–5% for men, 10–13% for women. Going below these levels causes hormonal, immune, and (in women) menstrual problems.

DEXA Scan

Dual-Energy X-ray Absorptiometry — the clinical gold-standard imaging method that separates fat, lean tissue, and bone. Error margin ±1–2% but costs $100–300 per scan and requires a radiology center.

Skinfold Caliper

A mechanical pincer that measures the thickness of subcutaneous fat at specific body sites (triceps, subscapular, abdomen). The Jackson-Pollock 3-site and 7-site protocols are the most common in gyms and sports labs.

ACE Categories

The five body fat percentage bands published by the American Council on Exercise: essential, athletes, fitness, average, and obese. Thresholds differ between men and women and are the most widely cited reference in consumer fitness.

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