Estimate your body fat percentage in seconds. Enter your age, gender, height, weight, neck, and waist (plus hip for women) to calculate Body Fat %, Fat Mass, and Lean Mass using the U.S. Navy circumference formula. Works with US (ft/in, lb) and Metric (cm, kg) units. Ideal for anyone ages 2–120 who wants a quick, science-based snapshot of body composition. Results are estimates and should be paired with professional guidance for training or health decisions.