Body Fat Calculator
What Is a Body Fat Calculator?
Body fat percentage is a far better measure of body composition than weight alone: two people can weigh exactly the same while one is lean and muscular and the other carries excess fat. Knowing your body fat percentage helps you set honest fitness goals, track whether a diet is burning fat rather than muscle, and understand your health risks more clearly than a scale ever could.
This calculator uses the well-known US Navy method, developed from military fitness research. It needs nothing more than a tape measure — no callipers, no expensive scan. You enter your height plus a few simple circumference measurements (neck, waist, and hip for women), and the formula estimates your body fat percentage. It is popular with gym-goers, athletes tracking a cut or bulk, and anyone whose BMI looks "off" because of muscle.
How to Use This Body Fat Calculator
- Choose your units. Tap "Metric" for centimetres or "Imperial" for inches.
- Select your gender. The formula differs for men and women; choosing female reveals the extra hip measurement field.
- Enter your height. Stand straight, barefoot, and measure from floor to the top of your head.
- Measure your neck. Tape just below the Adam's apple, keeping it level and snug but not tight.
- Measure your waist. At the navel for men; at the narrowest point of the waist for women. Breathe out normally — do not suck your stomach in.
- Women: measure your hips. Around the widest part of the buttocks, tape level all round.
- Click "Calculate Body Fat". You will get your estimated body fat percentage, your category, and a split of lean versus fat mass.
Worked Example: 178 cm Man
Here is the US Navy formula in action. Take a man who is 178 cm tall, with a 40 cm neck and an 88 cm waist:
- Waist minus neck: 88 − 40 = 48 cm
- First term: 86.010 × log10(48) = 86.010 × 1.68124 = 144.61
- Second term: 70.041 × log10(178) = 70.041 × 2.25042 = 157.62
- Combine: 144.61 − 157.62 + 36.76 = 23.7%
A result of 23.7% sits comfortably in the average band for men — healthy for everyday life, with room to move into the fitness band (14–17%) if that becomes the goal. The tool below does this arithmetic instantly; the example just shows you exactly what is happening under the hood.
Body Fat Categories
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
Tips for Accurate Measurements
- Measure in the morning. Your waist is smallest before breakfast; evening bloating can add a centimetre or two.
- Use a soft tape measure. A metal builder's tape will not sit flat; a tailor's tape costs almost nothing and works perfectly.
- Keep the tape level. Crooked tape is the biggest source of error — check in a mirror from the side.
- Measure three times. Take each measurement three times and use the average; consistency beats a single "perfect" reading.
- Track monthly, not daily. Real body composition changes slowly; monthly checks reveal the trend without the noise.
- Measure under the same conditions. Same time of day, same posture, same tape position — comparability is everything.
Frequently Asked Questions
How accurate is the US Navy body fat method?
It estimates within roughly ±3–4 percentage points of lab methods like DEXA scans for most people. It is less precise than a scan but far better than guessing, and it is excellent for tracking change over time — which is what matters for a fitness plan.
Why does the women's formula need a hip measurement?
Women typically store more fat around the hips and thighs, so the formula uses waist plus hip minus neck to capture that distribution. The men's formula only needs waist minus neck, since male fat storage is more concentrated around the abdomen.
What is a healthy body fat percentage?
For men, roughly 8–19% is considered healthy to fit; for women, about 21–33% depending on age. Athletes sit lower (6–13% men, 14–20% women). Very low levels can disrupt hormones, so lower is not automatically better.
Is body fat percentage better than BMI?
For body composition, yes — BMI cannot tell muscle from fat, while body fat percentage measures exactly what you want to know. A muscular person can have an "overweight" BMI with a perfectly healthy body fat percentage.
How often should I recalculate?
Once a month is ideal. Body composition shifts over weeks, not days, so monthly measurements under identical conditions give you a true trend line without daily noise.