Body Fat Calculator
US Navy Method · Metric & Imperial
yrs
ft
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Men: at the belly button. Women: at the narrowest point. Exhale normally.
in
Measure just below Adam's apple at narrowest point.
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cm
Men: at the belly button. Women: at the narrowest point. Exhale normally.
cm
Measure just below Adam's apple at narrowest point.
Enter your measurements to calculate body fat percentage.
Body Fat Percentage
0%
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Where You Fall
EssentialAthleteFitAverageObese
Body CompositionAmount
Body fat percentage—
Fat mass—
Lean mass—
Total body weight—
Body Fat Categories: Men
How Body Fat Is Calculated
Using the US Navy tape method, a 5'10" man with a 34 inch waist and a 15 inch neck has about 17.4% body fat, right at the line between the fitness and average ranges. The method needs only height, neck and waist (plus hips for women) and is usually within 3 to 4 points of a DEXA scan. Enter your measurements above for your percentage, fat mass and lean mass.
The US Navy circumference method was developed for rapid body fat assessment without expensive equipment. It uses neck and waist circumference (plus hips for women) to estimate body density, then converts to body fat percentage using the Siri equation. Accuracy is typically within 3-4% of DEXA scan results for most people.
Unlike BMI, body fat percentage distinguishes between fat mass and lean mass (muscle, bone, organs, water). Two people at the same weight and height can have dramatically different health risks depending on their body composition. A 180-pound person with 12% body fat is very different from one with 30% body fat: but BMI treats them identically.
| Category | Men | Women | Health Risk |
|---|---|---|---|
| Essential Fat | 2 to 5% | 10 to 13% | Minimal |
| Athlete | 6 to 13% | 14 to 20% | Very Low |
| Fitness | 14 to 17% | 21 to 24% | Low |
| Average | 18 to 24% | 25 to 31% | Moderate |
| Obese | 25%+ | 32%+ | High |
Why Women Have Higher Body Fat
Women naturally carry 6-11% more body fat than men at equivalent fitness levels. This is biologically essential for reproductive function, hormonal regulation (estrogen is produced in adipose tissue), thermal regulation, and pregnancy reserve. Essential fat for women is 10-13% vs 2-5% for men. Female athletes may reach 14-20% while competing at elite level.
Body Fat vs BMI
BMI correlates with body fat at only r ≈ 0.7, meaning significant individual variation exists. A muscular person may have BMI 27 (overweight) with 12% body fat. A sedentary person may have BMI 22 (normal) with 28% body fat: "skinny fat" or normal weight obesity, a real clinical concern associated with metabolic syndrome despite normal BMI.
Measurement Accuracy Tips
For best results: measure in the morning before eating. Use a flexible measuring tape, not a cloth tape that stretches. Take each measurement 3 times and average. Stand upright with relaxed muscles. Waist at the navel for men and at the narrowest point for women, neck below Adam's apple, hips at widest point (women). Consistent measurement technique matters more than single-point accuracy.
Other Measurement Methods
DEXA scan: reference method, typically within 1 to 2 points, expensive ($75-$200). Hydrostatic weighing: highly accurate, requires immersion tank. Bod Pod: air displacement, accurate, ~$50-100/session. Skinfold calipers: trained operator needed, ±3-4% accuracy. BIA scales: convenient but varies ±4-8% with hydration. Navy method: best free option for consistent tracking.
The US Navy Formula in Centimeters and Inches
The method was published in 1984 by Hodgdon and Beckett at the Naval Health Research Center. It estimates body density from circumferences, then converts density to body fat with the Siri equation (495 ÷ density − 450). The calculator uses the centimeter version:
- Men: 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
- Women: 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450
The military also uses an inch version with different constants, because the logarithm of an inch value is not the same as the logarithm of a centimeter value:
- Men: 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76
- Women: 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387
The two versions agree closely. For the 5'10" man in the example above the inch formula gives 17.5% against 17.4%. The mistake to avoid is plugging inches into the centimeter formula, which gives a wrong answer.
Body Fat by Waist Size: Reference Tables
Men, 5'10" with a 15 inch neck
| Waist at navel | Body fat |
|---|---|
| 30 in | 8.9% |
| 32 in | 13.4% |
| 34 in | 17.4% |
| 36 in | 21.1% |
| 38 in | 24.5% |
| 40 in | 27.7% |
| 42 in | 30.6% |
| 44 in | 33.4% |
Each inch off the waist takes about 1.5 to 2 points off the estimate in this range.
Women, 5'4" with a 13 inch neck
| Natural waist | Hips 36 in | Hips 40 in | Hips 44 in |
|---|---|---|---|
| 28 in | 23.7% | 28.9% | 33.9% |
| 30 in | 26.4% | 31.5% | 36.4% |
| 32 in | 28.9% | 33.9% | 38.7% |
| 34 in | 31.5% | 36.4% | 41.0% |
| 36 in | 33.9% | 38.7% | 43.3% |
| 38 in | 36.4% | 41.0% | 45.5% |
For women the waist and hips are added together, so an inch off either one moves the result by the same amount.
Worked Example and Measuring Mistakes
A 5'10" man (177.8 cm) with a 34 inch waist (86.36 cm) and 15 inch neck (38.1 cm): waist minus neck is 48.26 cm, and log10(48.26) = 1.6836. log10(177.8) = 2.2499. Density term: 1.0324 − 0.19077 × 1.6836 + 0.15456 × 2.2499 = 1.0590. Body fat: 495 ÷ 1.0590 − 450 = 17.4%. At 180 lb that is about 31 lb of fat and 149 lb of lean mass.
- Measuring women at the navel. The Navy method measures women at the natural waist, the narrowest point between the ribs and the navel, and men at the navel. Using the wrong spot shifts the result by several points.
- Tape too tight or too loose. The tape should sit flat on the skin without pressing in. Take each reading two or three times.
- Tilting the tape. Keep it level around the waist and hips. The neck tape can slope slightly down at the front, just below the larynx.
- Chasing small changes. A half-inch reading difference moves the estimate by about a point, so compare monthly averages rather than single days.
Treat the result as an estimate for tracking, not a diagnosis. A doctor or dietitian can help you interpret it. You can turn your percentage into lean mass with the lean body mass calculator.
Method and sources. US Navy circumference method: Hodgdon JA and Beckett MB, Naval Health Research Center (1984), with the Siri (1961) conversion from body density to body fat. Measurement sites follow the Navy multi-site protocol (men: neck and abdomen at the navel; women: neck, natural waist and hips). Every table value and the worked example were computed with the same centimeter formula the calculator uses; the inch version was checked against it. Category bands follow the American Council on Exercise chart shown above. Weight loss pace: CDC. Estimates only, not medical advice.
Body fat percentage calculations are estimates. The US Navy method has an error margin of approximately 3-4%. For precise assessment, use DEXA or hydrostatic weighing. This is not medical advice. Consult a healthcare professional for health guidance.
Frequently Asked Questions
Healthy ranges differ by sex and age. For men: essential fat 2-5%, athletes 6-13%, fitness 14-17%, average 18-24%, obese 25%+. For women: essential fat 10-13%, athletes 14-20%, fitness 21-24%, average 25-31%, obese 32%+. Women naturally carry more essential fat due to hormonal, reproductive, and thermoregulatory needs. The "fitness" range is generally considered optimal for health and performance in most adults.
The US Navy method is accurate within approximately 3-4% of DEXA scan results for most people of average build. It tends to overestimate body fat in very lean individuals and underestimate in those with high abdominal fat. The most accurate methods are DEXA scan (the usual reference method, typically within 1 to 2 percentage points), hydrostatic weighing (underwater weighing), and Bod Pod (air displacement plethysmography). The Navy method is the most accurate free, equipment-free method available and is reliable enough for tracking progress over time when measurements are taken consistently.
Waist: men measure horizontally at the level of the navel (belly button); women measure at the natural waist, the narrowest point between the ribs and the navel, as in the Navy protocol. Stand relaxed and upright, exhale normally, and do not suck in your stomach. Neck: measure just below the larynx (Adam's apple) at the narrowest point, with the tape slightly tilted downward at the front. Hips (women only): measure at the widest point around the buttocks with feet together. All measurements are best taken in the morning before eating. Take each measurement 3 times and use the average for best accuracy.
The US Navy formula uses logarithmic calculations. For men: Body Fat % = 495 / (1.0324 - 0.19077 × log10(waist - neck) + 0.15456 × log10(height)) - 450. For women: Body Fat % = 495 / (1.29579 - 0.35004 × log10(waist + hips - neck) + 0.22100 × log10(height)) - 450. All measurements are in centimetres. This formula estimates body density using circumference measurements, then applies the Siri equation (495/density - 450) to convert to body fat percentage.
Essential fat is the minimum body fat required for normal physiological function. In men, essential fat is approximately 2-5%. In women, it is 10-13% due to sex-specific fat in the breasts, uterus, and other reproductive tissues. Essential fat is critical for: insulating and protecting organs, nerve function (myelin sheaths are composed of fat), hormone production (sex hormones are derived from cholesterol, and estrogen is produced in adipose tissue), fat-soluble vitamin absorption (vitamins A, D, E, K), and thermoregulation. Going below essential fat levels leads to organ failure and is life-threatening.
Visceral fat is fat stored deep in the abdominal cavity, surrounding the organs (liver, pancreas, intestines). Unlike subcutaneous fat (under the skin), visceral fat is metabolically active and releases inflammatory cytokines and free fatty acids directly into the portal circulation. High visceral fat is strongly associated with insulin resistance, type 2 diabetes, cardiovascular disease, non-alcoholic fatty liver disease, and certain cancers: regardless of overall body weight or BMI. The waist circumference measurement in the Navy method partially reflects visceral fat accumulation, which is why abdominal girth is one of the most clinically important body composition measurements.
A safe and sustainable rate of fat loss is 0.5% to 1% of body weight per week. For most adults that is about 1 to 2 lb (0.5 to 0.9 kg) a week, the gradual pace the CDC recommends, which usually takes a daily deficit of roughly 500 to 1,000 calories. Faster loss increases the risk of losing lean muscle mass alongside fat. Preserving lean mass during weight loss requires adequate protein intake (1.6-2.2g per kg of body weight) and resistance training. Tracking body fat percentage rather than just scale weight gives a more accurate picture of whether you are losing fat or muscle.
Yes, significantly. Adults naturally gain body fat and lose lean muscle mass (sarcopenia) at approximately 3-8% of muscle mass per decade after age 30, accelerating after 60. This means a person can maintain the same body weight over decades while their body composition shifts substantially toward higher body fat and lower lean mass. This is why age-adjusted body fat percentage tables exist. What is considered acceptable body fat at 60 is higher than at 30. The American Council on Exercise (ACE) and other authorities publish age-stratified reference ranges for both men and women.
Elite athletes typically have very low body fat. Male distance runners: 4-10%. Male sprinters/cyclists: 4-14%. Female gymnasts: 10-16%. Male wrestlers/boxers (lean divisions): 4-8%. Female distance runners: 10-16%. American football linemen: 15-25% (weight and mass intentional). Bodybuilders in competition: 3-5% men, 8-12% women. Swimmers tend to be slightly higher body fat than other endurance athletes due to body insulation needs. Very low body fat can impair hormonal function. Female athletes who eat too little for their training load risk menstrual disruption and bone loss (the Female Athlete Triad). Male athletes below 5% may see impaired testosterone production.
BMI (Body Mass Index) is calculated from height and weight alone and makes no distinction between muscle and fat. Body fat percentage measures the actual proportion of your body composed of fat tissue. The key difference: two people with identical height and weight have identical BMI, but could have body fat percentages ranging from 10% (highly muscular) to 35% (low muscle, high fat). A muscular athlete classified as "overweight" by BMI may have 12% body fat and excellent metabolic health. A sedentary person with "normal" BMI may have 28% body fat and elevated cardiometabolic risk. Body fat percentage is a more diagnostically meaningful measure, though it requires measurement techniques beyond a scale and tape measure.
For men: 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76. For women: 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387, all in inches. It gives almost the same result as the centimeter version: a 5'10" man with a 34 inch waist and 15 inch neck gets 17.5% with the inch formula and 17.4% with the centimeter one.
With the Navy formula, about 1.5 to 2 percentage points per inch for a typical man. A 5'10" man with a 15 inch neck goes from 21.1% at a 36 inch waist to 17.4% at 34 inches. For women the waist and hips count together, so a 5'4" woman with 13 inch neck and 40 inch hips goes from 31.5% at a 30 inch waist to 28.9% at 28 inches. Remeasure every few weeks rather than daily.