Free Body Fat Calculator – Calculate Body Fat Percentage

How the Body Fat Calculator Works (US Navy Method)

Body fat percentage tells you what share of your total weight is fat rather than muscle, bone, organs, and water. This calculator estimates it with the U.S. Navy circumference method, developed by Hodgdon and Beckett for the Naval Health Research Center, which needs nothing more than a flexible tape measure and a few minutes. You enter your gender, height, and two or three body circumferences, and it returns your estimated fat percentage plus the category it falls into. That single figure answers a question the bathroom scale cannot: when your weight drops two kilograms, was it fat or was it muscle? Lifters running a cutting phase, people mid-way through a diet, anyone whose BMI reads high despite obvious muscle, and coaches who need a cheap repeatable measurement all use it. The formula is logarithmic rather than linear. For men: BF% = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450, with every measurement in centimetres. For women the equation adds hip circumference and uses different coefficients: BF% = 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450. The logic is that abdominal girth relative to neck size tracks stored fat closely, while height normalises for frame. Women get the extra hip term because they naturally carry more essential fat around the hips, and using the wrong gender setting will throw the estimate off by several points. Here is the arithmetic for a real man: 180 cm tall, 38 cm neck, 85 cm waist. Waist minus neck is 47 cm, and log10(47) is 1.672. log10(180) is 2.255. The denominator becomes 1.0324 − 0.19077 × 1.672 + 0.15456 × 2.255 = 1.06199. Divide 495 by that to get 466.11, subtract 450, and you land at 16.1 per cent body fat — the fitness range for a man. A woman at 165 cm with a 33 cm neck, 74 cm waist, and 98 cm hip gives waist plus hip minus neck of 139 cm; the denominator works out to 1.03571, so 495 ÷ 1.03571 − 450 = 27.9 per cent, which sits in the average band for women. The practical value shows up over weeks, not days. A man dieting from 88 kg to 84 kg checks his percentage at both ends: if it fell from 22 to 18 per cent, the loss was mostly fat and the plan is working. A rugby player with a BMI of 28 measures 12 per cent fat and can safely ignore the overweight label BMI gave him — the American College of Sports Medicine (ACSM) classifies this as an athletic-level body fat percentage. A woman who has held the same weight for three months but swapped cardio for strength work sees her percentage drop three points and finally has evidence the recomposition is happening. And someone deciding whether to keep cutting can see they are already near the lower healthy limit and should stop. Measurement technique is what makes or breaks this. Use a non-stretch tape, keep it level all the way round, snug against skin without denting it, and always measure at the same landmarks — neck just below the larynx, waist at the navel, hips at the widest point. The single biggest error beginners make is pulling the tape tight, which can shave three or four percentage points off the result and manufacture fake progress. Measure first thing in the morning before eating or drinking, take each reading twice, and compare only like-for-like sessions. The US Navy method is typically within three to four percentage points of a clinical reading and drifts further for very lean or very heavy people, so it is a trend tracker rather than a diagnosis; DEXA or hydrostatic weighing is the gold standard. This is informational, not medical advice. The calculation runs in your browser, so your measurements are never uploaded or stored.

Body Fat Calculator Formula & Method

Learn More — Body Fat Calculator Guide

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