BMI & Body Fat Percentage Calculator
Calculate your BMI and estimate body fat percentage from body measurements using the U.S. Navy circumference method. Useful for anyone who wants a more complete picture of body composition beyond simple weight.
About this calculator
Body Mass Index (BMI) is calculated as BMI = weight (kg) / height (m)². It provides a quick weight-for-height screening but does not distinguish between fat mass and muscle mass. To estimate body fat percentage, this calculator uses the U.S. Navy circumference method, which uses body measurements as proxies for fat distribution. For males: Body Fat% = 495 / (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450. For females the formula also incorporates hip circumference. The method was developed by Hodgdon and Beckett and has been validated against hydrostatic weighing. While not as precise as DEXA scanning, it provides a practical, equipment-free estimate that goes well beyond what BMI alone reveals, particularly for muscular individuals whose BMI may over-classify them as overweight.
How to use
Consider a male weighing 80 kg, 175 cm tall, with a neck circumference of 38 cm. Step 1 — BMI: 80 / (1.75)² = 80 / 3.0625 ≈ 26.1 (slightly overweight range). Step 2 — Body fat (Navy method): convert measurements and apply the male formula. Using the provided formula values, the log terms are computed from the waist-minus-neck and height measurements. For a 35-year-old male at these dimensions, the estimate typically yields a body fat percentage in the 18–22% range. Entering all values into the calculator delivers both BMI classification and a precise body fat estimate in seconds.
Frequently asked questions
What is the difference between BMI and body fat percentage, and which is more accurate?
BMI is purely a ratio of weight to height squared and gives no information about whether that weight comes from fat, muscle, or bone. Body fat percentage directly measures the proportion of your mass that is adipose tissue, making it a far more meaningful health metric. A bodybuilder, for example, might have a BMI in the 'overweight' range despite very low body fat. For health assessments, body fat percentage is considered more accurate and informative, though both metrics have limitations when used in isolation.
What are healthy body fat percentage ranges for men and women?
Healthy body fat ranges differ significantly by sex due to hormonal and physiological differences. For men, essential fat is around 2–5%, athletic range is 6–13%, fitness range is 14–17%, acceptable range is 18–24%, and obesity begins above 25%. For women, essential fat is 10–13%, athletic is 14–20%, fitness is 21–24%, acceptable is 25–31%, and obesity begins above 32%. These ranges also shift slightly with age, as body fat naturally increases and muscle mass decreases over time. Context — activity level, age, and health history — should always inform how you interpret your result.
How does the U.S. Navy body fat method compare to DEXA scanning?
The U.S. Navy circumference method is a field-expedient technique requiring only a tape measure, making it accessible and free. Studies show it has a margin of error of approximately 3–4 percentage points compared to laboratory methods. DEXA (Dual-Energy X-ray Absorptiometry) scanning is considered the gold standard for body composition analysis, distinguishing bone mass, lean tissue, and fat tissue with high precision, but it requires medical equipment and carries a small radiation exposure. For most people tracking body composition over time, the Navy method is sufficiently accurate — consistent measurement technique matters more than the absolute number.