Body Fat Calculator

Body fat percentage tells you what fraction of your weight is fat tissue rather than muscle, bone, water, and organs. Two people can weigh exactly the same and look completely different because one carries more lean mass and the other carries more fat, and the scale alone cannot tell them apart. That single number — your weight — silently averages everything together. Body fat percentage pulls the curtain back on that average: it separates the part of you that is metabolically quiet from the part that is working tissue, and it answers the question the bathroom scale keeps dodging, which is not "how heavy am I?" but "what am I made of?" For anyone tracking fitness, weight loss, or general health, it is usually a more honest signal than weight alone, because it reflects composition rather than just quantity.

This calculator uses the U.S. Navy circumference method, a formula developed by the Navy to estimate body fat in recruits without expensive lab equipment. Instead of weighing you underwater or scanning you with X-rays, it takes a handful of simple tape measurements — height, neck, and waist, plus hip for women — and feeds them through a logarithmic equation. The insight behind the method is that fat tends to gather in predictable places relative to bone and muscle, so the difference between your waist and neck circumferences, combined with your height, is a surprisingly good proxy for overall body fat. It is not a direct measurement like a DEXA scan, but for a free tool that runs entirely in your browser, it lands close enough to be genuinely useful for spotting trends week to week. The formula differs slightly for men and women because average fat distribution differs between the sexes, which is exactly why the calculator asks for hip circumference only when "Female" is selected. The accuracy of any circumference method lives or dies by the tape, not the math, so a little care up front pays off. Measure your neck just below the larynx, with the tape level and not squeezed into the skin. For the waist, wrap the tape at the navel rather than at the narrowest point of your torso — the formula expects the navel reading, and using the "smallest" spot will quietly throw the result off. Women should measure the hip at its widest point, usually around the buttocks. Keep the tape snug but not pinching, breathe normally, and stand relaxed rather than flexing. Because the method is sensitive to small differences, it helps to measure at the same time of day and in similar clothing each time; first thing in the morning before eating is a dependable habit. One solid reading is better than five sloppy ones, and consistency across weeks matters far more than hitting a perfect number on any single attempt. When you calculate, you get three things: your estimated body fat percentage, your fat mass, and your lean mass, plus a category label that places the percentage into a rough range such as athlete, fitness, average, or obese. These ranges are useful for orientation but should never be read as a medical verdict — they are population averages, not a diagnosis, and the cut-offs shift between men and women. Treat the percentage as a compass, not a scoreboard: a single reading tells you little, but the direction it moves over a month of training or dieting tells you a great deal. The method works best as a trend tracker rather than a one-time test, because its margin of error is a few percentage points compared with clinical methods like DEXA or hydrostatic weighing. If you want the broader context for the energy behind your body, the BMR and calorie calculators on this site turn your stats into daily calorie estimates, and the water-intake calculator adapts your hydration target to your body size — all built from the same height, weight, age, and sex inputs you already entered here.

The two outputs beyond the percentage — your fat mass and lean mass — are what make this calculator useful for planning, not just assessment. Lean mass is the part you generally want to protect or build, because it is the metabolically active tissue that supports your BMR and your strength, while fat mass is the part most people aim to reduce. Say your result shows 16.5 kg of fat and you would like to sit at a body-fat percentage closer to 25 percent; because lean mass stays roughly steady while you diet, you can work backward to a target weight rather than guessing. Keeping lean mass stable also means the scale can move less than you expect even as you get leaner, which is exactly why tracking body fat trends matters more than daily weigh-ins. The honest takeaway is that a single reading is a snapshot, but paired with a clear target it becomes a route: measure monthly, watch the fat-mass line fall and the lean-mass line hold, and let the trend — not one fluctuating number — guide your next adjustment.