Body Fat Calculator
Estimate body fat percentage using the US Navy circumference method.
Cómo funciona
This calculator estimates body fat percentage using the US Navy circumference method, developed by the US Navy in the 1980s as a practical, equipment-free alternative to more precise but harder-to-access methods like hydrostatic weighing.
It works from simple tape-measure circumferences — neck and waist for men, plus hip for women — combined with height, in a logarithmic formula (log-based, since body fat doesn't scale linearly with circumference measurements). You don't need to know the formula's internals to use the calculator; entering the three or four measurements is enough.
Body fat percentage ranges considered healthy differ by sex, reflecting natural biological differences in essential fat: roughly 10–20% is typical for fit men, and 18–28% for fit women, with athletes often landing below those ranges and higher percentages indicating increasing health risk, particularly above roughly 25% for men and 32% for women.
The circumference method's biggest advantage is accessibility — no special equipment beyond a measuring tape — but it's inherently less precise than clinical methods like DEXA scans (a type of X-ray body composition scan), hydrostatic (underwater) weighing, or skinfold calipers with a trained technician, all of which directly or more precisely estimate fat versus lean tissue rather than inferring it from circumference alone.
Body fat percentage is generally a more meaningful health indicator than weight or even BMI alone, since it distinguishes fat mass from lean mass (muscle, bone, organs, water) — two people at an identical weight and height can have very different body fat percentages and correspondingly different health profiles.
During a fitness program, tracking body fat percentage over time tends to be more informative than tracking scale weight alone — it's possible to lose fat and gain muscle simultaneously with little net change in total weight, a pattern that would look like "no progress" on a scale but represents real, positive body composition change.
How accurate is this method?
It's a reasonable estimate for most people but less precise than DEXA scans or hydrostatic weighing.
Why might my weight stay the same even though my body is changing?
Simultaneous fat loss and muscle gain can offset each other on the scale — body fat percentage tracks this kind of composition change even when total weight barely moves.
Why does the formula need different measurements for men and women?
Women's formula includes hip circumference in addition to neck and waist, reflecting typical sex differences in where body fat tends to accumulate.
What's a healthy body fat percentage range?
Roughly 10–20% for fit men and 18–28% for fit women is typical, though healthy ranges vary by age, fitness level, and individual factors — these are general guidelines, not strict cutoffs.
Why is body fat percentage more useful than BMI?
BMI can't distinguish muscle from fat, while body fat percentage measures the fat/lean tissue split directly, giving a more meaningful picture of body composition for the same height and weight.
What's the most accurate way to measure body fat?
DEXA scans are generally considered a gold-standard clinical method, with hydrostatic weighing also highly accurate — both require specialized equipment unavailable at home, unlike the tape-measure method here.
How should I measure my waist and neck accurately?
Measure at the specific points the calculator's instructions describe (typically waist at the navel, neck just below the larynx), keeping the tape snug but not compressing the skin, for the most consistent results.
Can body fat percentage be too low?
Yes — essential fat (roughly 2–5% for men, 10–13% for women) is required for basic physiological function; going below healthy minimums can cause serious health problems.
Does this method work well for very muscular or very lean individuals?
It tends to be less accurate at the extremes of muscularity or leanness, since the formula was calibrated on general population data rather than athletic outliers.
How often should I re-measure my body fat percentage?
Every few weeks is reasonable for tracking meaningful change — day-to-day fluctuations from water retention and measurement inconsistency make daily tracking mostly noise rather than signal.