Body Fat Calculator

Last updated: April 5, 2026

The Body Fat Calculator estimates your body fat percentage using the US Navy circumference method — measuring neck, waist, and hips — without expensive equipment. Body fat percentage tells you what fraction of your weight is fat versus lean mass, giving a more useful health picture than BMI alone.

Calculator

Sex

Waist Circumferencecm

Neck Circumferencecm

Heightcm

Hip Circumferencecm

Results

Body Fat

16.9

Fat Mass per 100 kg Body Weight

16.9

Lean Mass per 100 kg Body Weight

83.1

Results

Body Fat

16.9

Fat Mass per 100 kg Body Weight

16.9

Lean Mass per 100 kg Body Weight

83.1

BMI tells you whether your weight-to-height ratio is in a healthy range. Body fat percentage tells you whether that weight is fat or muscle — and the difference is everything. Two people can have identical BMIs with completely different body compositions and completely different health risk profiles. The body fat calculator uses the US Navy method — validated against hydrostatic weighing — to estimate your body fat percentage from simple tape measure inputs.

US Navy Body Fat Formula

The US Navy method uses body circumferences to estimate body fat:

Men: BF% = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76

Women: BF% = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387

All measurements in centimeters. Measure: waist at narrowest point (men) or at navel (women); neck just below the larynx; hips at widest point (women only). Use this online calculator to compute your body fat instantly. The lean body mass calculator converts your result to absolute lean and fat mass.

Healthy Body Fat Ranges by Sex and Age

American Council on Exercise (ACE) body fat classification:

Men — Essential fat: 2–5%; Athlete: 6–13%; Fitness: 14–17%; Average: 18–24%; Obese: 25%+
Women — Essential fat: 10–13%; Athlete: 14–20%; Fitness: 21–24%; Average: 25–31%; Obese: 32%+

Body fat naturally increases with age — a 55-year-old at 22% fat may be in the same health category as a 25-year-old at 18%. The Army body fat calculator uses the same Navy method with military-specific standards.

Navy Method vs. Other Body Fat Measurement Techniques

US Navy circumference method: ±3–4% accuracy vs. DEXA; free, no equipment needed; good for tracking trends
Skinfold calipers (Jackson-Pollock 3 or 7 site): ±3–5% with trained technician; cheap but skill-dependent
Bioelectrical impedance (BIA): ±3–5% under controlled conditions; highly sensitive to hydration status
DEXA scan: ±1–2%; gold standard for clinical use; requires medical imaging equipment
Hydrostatic (underwater) weighing: ±1–3%; very accurate; time-consuming and requires immersion tank
BOD POD (air displacement plethysmography): ±2–3%; accurate and quick; available at sports performance centers

For most people, the Navy method is accurate enough to set goals and track progress. If you need precise individual body composition data for medical or sports performance purposes, DEXA or BOD POD is recommended. The BAI calculator and body composition calculators provide complementary assessment tools.

Body Fat Percentage vs. BMI: Why Both Matter

BMI and body fat percentage capture different things. A muscular person with BMI 28 and 12% body fat has very different health risks than a sedentary person with BMI 28 and 32% body fat — yet BMI alone cannot distinguish them. Body fat percentage catches "normal weight obesity" — people with normal BMI but high fat percentage — who carry elevated metabolic risk that BMI misses entirely. For the most complete picture: use BMI for quick population-level screening; use body fat percentage for understanding actual body composition; add waist circumference to capture fat distribution (abdominal vs. peripheral).

Visual Analysis

How It Works

Enter height, neck circumference, waist circumference (at narrowest for men, at navel for women), and hip circumference (women only). Men: BF% = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76. Women: BF% = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387. All measurements in cm. Fat mass = weight × BF%; lean mass = weight − fat mass.

Worked Examples

Example 1

Inputs

Results

Example 2

Inputs

Results

Frequently Asked Questions

Healthy body fat ranges differ significantly by sex and age. For men: essential fat is 2–5% (minimum for organ function); athletic range 6–13%; fitness range 14–17%; acceptable average 18–24%; above 25% is considered obese by ACE standards. For women: essential fat is 10–13% (includes sex-specific fat in breasts and uterus); athletic range 14–20%; fitness range 21–24%; acceptable average 25–31%; above 32% is classified obese. Body fat naturally increases with age — a 60-year-old at 25% body fat may be in the same relative health category as a 30-year-old at 20%. Military standards are stricter: US Army requires men aged 17–20 to be below 20% body fat; women the same age below 30%.

The US Navy circumference method has an accuracy of approximately ±3–4% body fat compared to the gold standard of DEXA (dual-energy X-ray absorptiometry) or hydrostatic weighing. In the original validation studies by Hodgdon and Beckett (1984), it correctly classified approximately 75–80% of subjects within 3.5% of their actual body fat. The method is more accurate for people in the middle range (10–30% body fat) and less accurate at extremes (very lean or very obese individuals). Measurement technique matters significantly: inaccurate tape placement can shift results by 2–5%. Take three measurements at each site and average them for best results.

For the US Navy method — Neck: measure at the narrowest point, just below the larynx (Adam's apple); keep the tape level and perpendicular to the neck; look straight ahead during measurement. Men — Waist: measure at the narrowest point of the abdomen (usually 1 inch above the navel), after a normal exhale; do not suck in or push out. Women — Waist: measure at the navel level. Women — Hips: measure at the widest point of the buttocks and hips. All measurements: keep the tape parallel to the floor; do not compress the skin; take 3 readings and use the average. Consistent technique between measurements is more important than any individual reading — it ensures your tracking over time is meaningful.

Essential fat is the minimum amount of fat required for normal physiological function — it is found in the brain, nerves, bone marrow, organs, and cell membranes, and in women includes sex-specific fat in breast tissue, the uterus, and other reproductive structures. For men, essential fat is approximately 2–5% of body weight; for women, 10–13%. Storage fat is the fat deposited in adipose tissue (under the skin and around organs) that serves as an energy reserve and thermal insulation. The excess storage fat above the essential minimum is what most people aim to reduce when losing weight. Reducing body fat below essential levels causes hormonal disruption, immune impairment, bone loss, and organ damage — for women, this commonly manifests as menstrual irregularity.

No — spot reduction (losing fat from a specific body part through targeted exercise) is not supported by evidence. Fat mobilization is systemic — your body draws on fat stores throughout the body based on hormonal signals and genetics, not based on which muscles are working. Ab exercises build abdominal muscle but do not preferentially burn abdominal fat. The only proven approaches to reducing body fat in any specific area are: overall caloric deficit to reduce total body fat (which will gradually reduce fat everywhere, including problem areas); resistance training to increase lean muscle and raise metabolic rate; in extreme cases, liposuction (which removes fat cells but does not prevent future fat accumulation). Genetics heavily influence where your body stores and loses fat first.

The most evidence-based approach combines caloric deficit with resistance training. Caloric deficit (eating 300–500 kcal/day below your TDEE) causes fat loss — at a rate of approximately 0.3–0.7 kg of fat per week at these deficits. Resistance training preserves lean muscle mass during weight loss, which is critical because without it approximately 25–35% of weight lost in a caloric deficit comes from lean tissue rather than fat. Adequate protein intake (1.6–2.2 g/kg body weight per day) further protects lean mass during a deficit. Adding aerobic exercise increases the caloric deficit without requiring further dietary restriction. Key point: rate of fat loss matters — very aggressive deficits (over 750 kcal/day) accelerate muscle loss, lowering your body fat percentage less efficiently than moderate deficits.

Sources & Methodology

Hodgdon, J.A., Beckett, M.B. (1984). Prediction of percent body fat for US Navy men from body circumference and height. NHRC Report 84-11. Friedl, K.E. et al. (1992). Evaluation of anthropometric equations to assess body composition changes. American Journal of Clinical Nutrition. ACE (2009). Percent Body Fat Norms for Men and Women.

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