Body Fat Calculator

How the U.S. Navy body fat formula works

The Navy circumference method estimates body fat by combining height with one or more circumference measurements. Men enter neck and waist, while women enter neck, waist, and hips to account for typical fat distribution patterns. We apply logarithmic equations to those measurements, convert everything to the same unit system, and output body fat percentage alongside your estimated fat mass and lean mass.

Tips for accurate measurements

• Use a flexible fabric tape and measure against bare skin for consistency.
• Take measurements at the same time of day, ideally after waking and before eating.
• Place the tape at the narrowest part of your neck and at the level of your navel for the waist.
• For hips, measure the widest point across the glutes while keeping the tape parallel to the floor.

Interpreting your body fat percentage

Healthy ranges vary by age and sex, but generally men feel best between 10–20% and women between 18–28%. Lower percentages often align with athletic performance, while higher percentages can increase the risk of metabolic and cardiovascular issues. Track trends over weeks, not days—hydration, recent workouts, and meal timing can all shift circumference measurements temporarily.

Remember the limitations

Circumference methods are estimates and can be skewed by posture, muscle mass, and where you store body fat. If you strength train heavily, the calculation may overstate fat mass. When in doubt, compare with other tools such as progress photos, strength benchmarks, or a professional DEXA scan to understand your full body composition picture.

Pair the calculator with BiteCheck to log measurements, visualize changes over time, and get nutrition suggestions that match your body composition goals.