Enter your neck, waist, and hip circumferences (women only) along with height. The U.S. Navy formula gives a reliable body fat estimate — including your category, fat mass, lean mass, and how far you are from your ideal range.
U.S. Navy formula Men & women Metric & imperial Fat mass & lean mass Body fat category Fat-to-lose estimate
Body Fat Calculator
U.S. Navy circumference method
Gender
Units
yrs
kg
cm
Height (ft / in)
ft
in
cm
Measure just below the Adam's apple (larynx)
cm
Men: at navel level · exhale normally before measuring
cm
Widest point of hips/buttocks — tape horizontal all around
Body Fat
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—
Fat Mass
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Lean Body Mass
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Ideal BF% Range
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Fat to Lose for Fitness Category
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Body Fat Calculator — U.S. Navy Formula for Men & Women
This free body fat calculator uses the U.S. Navy circumference method to estimate your body fat percentage from simple tape measurements. Unlike BMI — which only uses weight and height — this method measures circumferences at key points where fat actually accumulates, giving a more accurate picture of your body composition.
Results include your body fat percentage, ACE category (essential fat / athlete / fitness / average / obese), fat mass in kg or lb, lean body mass, and the fat loss needed to reach the top of your ideal category.
The U.S. Navy Body Fat Formula
Developed by the U.S. Navy and widely used in military fitness assessments, the formula uses neck, waist, and (for women) hip circumferences alongside height:
All measurements in centimetres. Imperial inputs are converted to cm before calculation.
Example (male): Waist 85 cm, Neck 38 cm, Height 178 cm
= 86.010 × log₁₀(85 − 38) − 70.041 × log₁₀(178) + 36.76
= 86.010 × 1.672 − 70.041 × 2.250 + 36.76 = ≈ 15.8%
How to Take Accurate Measurements
The U.S. Navy formula is only as accurate as your measurements. Follow these guidelines for consistent, reliable results:
NeckMeasure just below the larynx (Adam's apple), perpendicular to the axis of the neck. Keep the tape snug but not compressing skin. Look straight ahead.
WaistMen: at the level of the navel. Women: at the narrowest point of the abdomen (usually between navel and ribs). Measure at the end of a normal exhale — don't hold your breath or pull in your stomach.
Hip (women only)Measure at the widest point of the hips/buttocks, keeping the tape horizontal all the way around. Stand with feet together for consistency.
General tipsUse a flexible cloth or plastic measuring tape. Take measurements twice and average them. Measure at the same time of day (morning before eating is most consistent). Wear minimal clothing.
Body Fat Percentage Categories (ACE Standards)
The American Council on Exercise (ACE) defines five body fat categories for adults:
Category
Men (%)
Women (%)
Notes
Essential Fat
2 – 5%
10 – 13%
Minimum needed for organ function. Not a sustainable target for most people.
Athletes
6 – 13%
14 – 20%
Typical of competitive athletes and serious gym-goers.
Fitness
14 – 17%
21 – 24%
Associated with an active, health-conscious lifestyle.
Average
18 – 24%
25 – 31%
Typical of the general population. Health risk low to moderate.
Obese
≥ 25%
≥ 32%
Elevated health risk. Cardiovascular, metabolic, and joint stress.
Women naturally carry more body fat than men at equivalent fitness levels due to hormonal requirements (oestrogen) and reproductive physiology. The ACE standards account for this with separate thresholds.
Body Fat % vs BMI — What's the Difference?
Both metrics assess whether you have a healthy body composition, but they measure very different things:
Metric
What it measures
Best for
Limitation
BMI
Weight relative to height
Population-level screening, quick assessment
Can't distinguish muscle from fat — misclassifies athletes
Body Fat %
Actual proportion of fat in body weight
Body composition tracking, fitness assessment
Requires accurate measurements; Navy formula has ±3–4% error
A muscular athlete can have a "overweight" BMI of 27 yet a lean body fat of 12%. Conversely, a sedentary person with a "normal" BMI of 22 might have a body fat of 28% — sometimes called skinny fat or normal-weight obesity — with elevated metabolic risk despite a normal weight.
How to Reduce Body Fat Effectively
Calorie DeficitFat loss requires consuming fewer calories than you burn. A deficit of 500 kcal/day produces ~0.45 kg of fat loss per week. Calculate your TDEE first using the BMR calculator, then eat below it.
High Protein IntakeProtein preserves lean muscle during a deficit and is more satiating than carbs or fat. Aim for 1.6–2.2 g/kg of body weight per day when trying to lose fat.
Resistance TrainingStrength training during fat loss preserves or even builds muscle mass, improving body composition beyond what the scale or body fat % shows. Aim for 3–4 sessions per week.
Cardio & NEATAerobic exercise burns calories and improves cardiovascular health. Non-exercise activity thermogenesis (NEAT) — walking, standing, fidgeting — contributes more to daily calorie burn than most gym sessions.
Frequently Asked Questions
Body fat percentage is the proportion of your total weight made up of fat tissue. A person weighing 80 kg with 20% body fat has 16 kg of fat and 64 kg of lean mass (muscle, bone, water, organs). It's a more meaningful health metric than weight alone.
The U.S. Navy circumference method — developed by the U.S. Naval Health Research Center. It uses neck, waist, and (for women) hip circumferences alongside height. The formula uses log₁₀ of measurement differences, making it reasonably accurate without requiring any equipment beyond a tape measure.
Studies show the U.S. Navy method has a standard error of approximately ±3–4% compared to DEXA (dual-energy X-ray absorptiometry), the gold standard. It's more accurate than BMI for body composition and significantly easier than skinfold calipers. The main sources of error are inconsistent measurement technique and atypical fat distribution patterns.
Men and women store fat differently. Men predominantly store fat abdominally (visceral fat, measured at the waist). Women store more fat in the hips and thighs (gluteofemoral fat). The Navy formula accounts for this by using hip circumference in the female equation to capture this typical fat distribution pattern.
According to ACE standards: Fitness range for men is 14–17%; for women it's 21–24%. Athlete range is lower (6–13% men, 14–20% women). Going below essential fat levels (2–5% men, 10–13% women) is dangerous. Most health guidelines consider the fitness and average categories (up to 24% for men, 31% for women) as acceptable for non-athletes.
Yes — this is one of the best uses of the calculator. While any single measurement has some error, the trend over time is meaningful. Take measurements at the same time of day (morning, before eating) and in the same conditions each time. Track monthly rather than weekly for most meaningful trends.
Lean body mass (LBM) is everything in your body that isn't fat — muscles, bones, organs, water, and connective tissue. LBM = total weight × (1 − body fat%). It's metabolically active tissue that burns calories at rest and is the goal to preserve during fat loss.
For the most accurate body composition assessment: DEXA scan (most accurate, medical-grade); hydrostatic weighing (very accurate); 3D body scanner (good accuracy, increasingly available at gyms); Bod Pod (air displacement plethysmography); skinfold calipers (technique-dependent); bioelectrical impedance (convenient but affected by hydration). The Navy method compares favourably to calipers and BIA for everyday use.
