Body Fat Calculator
Body fat percentage tells you what weight cannot: how much of you is fat and how much is everything else. This calculator uses the US Navy circumference method, which needs only a tape measure and gets within a few percentage points of far more expensive scans when the measurements are taken carefully.
Inputs
Result
16.9 %
How the body fat calculator works
The Navy method uses logarithms of circumferences: for men, neck and waist relative to height; for women, neck, waist and hips relative to height.
Fat mass = body weight × body fat percentage. Lean mass is the remainder, which is the figure worth tracking during a diet.
General bands for men: 6–13% athletic, 14–17% fit, 18–24% acceptable, 25%+ obese. For women add roughly 8–10 points to each band, because essential fat is higher.
Worked example: a man, 178 cm, 82 kg
- Neck 38 cm, waist 92 cm. Waist minus neck = 54 cm.
- Navy formula returns approximately 21.5% body fat.
- Fat mass: 82 × 0.215 = 17.6 kg. Lean mass: 64.4 kg.
- Losing 6 kg of pure fat would give 76 kg at 15.3% — a visible change with no lean loss.
- If the same 6 kg loss included 1.5 kg of muscle, body fat would only reach 17.2%.
Common mistakes to avoid
Measuring the waist in the wrong place
Use the narrowest point for women and at the navel for men, tape level and skin uncompressed. A 2 cm error moves the result by roughly 1.5 percentage points.
Measuring at different times of day
Bloating and hydration shift waist circumference. Measure first thing in the morning, before eating, every time.
Chasing very low percentages
Below about 6% for men and 14% for women, hormonal and immune function degrades. Low is not automatically better.
Frequently asked questions
How accurate is the Navy method?
Typically within 3–4 percentage points of a DEXA scan when measurements are careful. Its consistency over time is more valuable than its absolute accuracy.
What is a healthy body fat percentage?
Roughly 10–20% for men and 18–28% for women, with athletic ranges lower. Essential fat is about 3% for men and 12% for women.
Why does my smart scale disagree?
Bioelectrical impedance scales estimate from hydration-sensitive resistance and can swing several points day to day. Use one method consistently.
Can I lose fat without losing weight?
Yes — body recomposition. Beginners and those returning to training often gain muscle while losing fat, so weight stalls while measurements improve.
Where does the body lose fat first?
Distribution is genetic and cannot be targeted by exercise selection. Overall deficit determines fat loss; the order is not under your control.
Learn more
Body fat vs BMI: why the scale misreads a muscular body
Two people, same height, same weight, completely different health profiles. BMI cannot tell them apart.
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