Body Fat Calculator
This free Body Fat Calculator estimates your body fat percentage using the US Navy method, BMI-based formula, and optional skinfold measurements. Enter your height, weight, waist, neck, and (for women) hip measurements to calculate body fat %, fat mass, and lean body mass. The Navy method is one of the most accessible and reliable estimation techniques, while the BMI and Covert Bailey formulas provide additional reference points. For fitness and training use, you can enable 3-site or 7-site skinfold measurements for more detailed accuracy. Everything runs instantly in your browser, with no data stored or sent anywhere.
What Is a Body Fat Calculator?
A body fat calculator estimates your body fat percentage using circumference measurements (US Navy method), BMI, or skinfold equations. Body fat % is the proportion of your total weight that is fat mass; the remainder is lean mass (muscle, bone, organs, water). Unlike BMI, body fat % distinguishes between fat and muscle — a 180 lb athlete at 10% body fat and a 180 lb sedentary person at 28% have the same BMI but dramatically different health profiles. The US Navy method is the most widely used free method, requiring only height, neck, and waist measurements (and hips for women).
Body Fat Percentage Categories by Sex
| Category | Men | Women | Description |
|---|---|---|---|
| Essential Fat | 2–5% | 10–13% | Minimum required for survival |
| Athletic | 6–13% | 14–20% | Elite athletes, bodybuilders |
| Fit | 14–17% | 21–24% | Regular exercisers |
| Average | 18–24% | 25–31% | General population |
| Obese | 25%+ | 32%+ | Increased health risk |
Women naturally carry 5–10% more essential fat than men due to reproductive hormones. Athletes may be in the Athletic category without any health risks.
Body Fat Measurement Methods Compared
| Method | Accuracy | Cost | Best For |
|---|---|---|---|
| DEXA Scan | ±1–2% | $$$ | Gold standard reference |
| Hydrostatic Weighing | ±2–3% | $$ | Athletes, research |
| Skinfold Calipers | ±3–4% | $ | Tracking changes over time |
| Bioimpedance (BIA) | ±3–5% | $ | At-home convenience |
| US Navy Method | ±3–5% | Free | Quick estimates anywhere |
| BMI-Based | ±5–10% | Free | Population screening only |
Worked Example: Mike’s Body Composition
30M, 5'10" (178 cm), 180 lbs | Waist: 34" | Neck: 16"
US Navy: 86.010 × log₁₀(34−16) − 70.041 × log₁₀(70) + 36.76 = 18.5% body fat
Category: Fit | Fat Mass: ~33 lbs | Lean Mass: ~147 lbs
Despite BMI of 25.8 (Overweight), Mike is metabolically in the Fit category by body composition
Why Body Fat % Matters More Than BMI
BMI classifies weight relative to height but can’t distinguish muscle from fat. A 200 lb, 6’ bodybuilder with 8% body fat has a BMI of 27.1 (Overweight); a 160 lb sedentary person with 35% body fat may have a BMI of 21.7 (Healthy). Body fat % reveals the true composition. Visceral fat (fat around organs, concentrated in the abdominal area) is the most metabolically dangerous type — waist circumference above 35″ (women) or 40″ (men) signals elevated cardiovascular risk regardless of BMI. Reducing body fat from 30% to 22% while maintaining weight through muscle gain dramatically improves insulin sensitivity, cholesterol, and inflammatory markers.
Frequently Asked Questions About Body Fat %
How accurate is the US Navy body fat method?
The US Navy method has an accuracy of ±3–5% compared to DEXA scans. It tends to underestimate body fat in very lean individuals and overestimate in people with unusual fat distribution. Consistent measurement technique (measuring at the same time of day, same hydration state) is more important than which method you use — tracking the trend over time is what matters.
What is a healthy body fat percentage?
For men: 14–17% is Fit, 18–24% is Average. For women: 21–24% is Fit, 25–31% is Average. Most health organizations consider anything below 25% (men) and 32% (women) as non-obese. Optimal body fat for longevity research tends to cluster in the Fit range rather than the Athletic range, since very low body fat has its own health risks.
Can body fat % be too low?
Yes. Essential fat is the minimum required for physiological function: 2–5% for men, 10–13% for women. Going below essential fat levels causes hormonal dysfunction, immune suppression, bone loss, and in women, loss of menstrual function (female athlete triad). Competitive bodybuilders routinely reach dangerously low levels (3–5% men, 8–10% women) for brief contest periods only.
How do I reduce body fat percentage?
Body fat % is reduced by losing fat mass while preserving or gaining lean mass. A 500 calorie/day deficit with 0.7–1g protein per lb of body weight, combined with resistance training, is the evidence-based approach. Cardio accelerates fat loss but excessive cardio without adequate protein causes muscle loss, which can leave body fat % unchanged even as weight drops.
How often should I measure body fat?
Measure every 4–6 weeks, not daily. Body fat methods have inherent measurement error of 3–5%, so daily fluctuations are noise, not signal. Track trends over months. Consistent measurement conditions (morning, fasted, same hydration) minimize variability.
Does age affect body fat percentage?
Yes. Aging causes muscle loss (sarcopenia) and fat redistribution — people maintain the same weight but gradually accumulate fat as muscle decreases. A 50-year-old may have the same BMI as at 30 but 5–10% more body fat. Resistance training is the most effective intervention to counteract age-related body composition changes.
Related Calculators
BMI Calculator
BMI chart and healthy weight range by height
Lean Body Mass Calculator
LBM using Boer, James, and Hume formulas
Ideal Weight Calculator
Healthy weight range by formula comparison
Army Body Fat Calculator
US Army tape test and military standards
One Rep Max Calculator
Calculate 1RM and training percentages
BAC Calculator
Blood alcohol content and sobriety estimator