🧬 Body Fat Calculator
Estimate your total body fat percentage based on your BMI, age, and gender parameters.
Estimating body fat percentage, and how far to trust the number
Body fat percentage is the share of your total weight that is fat rather than muscle, bone, organs and water. It answers the question BMI cannot: not how heavy you are, but what you are made of. Two people at the same weight and height can differ by twenty percentage points of body fat and have completely different health profiles.
Every method short of a laboratory scan is an estimate. The calculator above offers two: the US Navy circumference method, which uses tape measurements, and a BMI-derived formula. The first is considerably more reliable.
The US Navy method
Developed for military fitness assessment, it uses the relationship between girth measurements and body density. It needs height, neck and waist for men, with hip added for women:
Men: %fat = 495 / (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
Women: %fat = 495 / (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450
Measurements are in centimetres. Accuracy is typically within three to four percentage points of a DEXA scan for people of average build, and it drifts further for the very lean and the very heavy. Measure first thing in the morning, relaxed, with the tape snug but not compressing the skin.
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% and above | 32% and above |
Women's ranges sit roughly ten points higher throughout, and this is physiological rather than a matter of fitness: essential fat supports hormonal and reproductive function. Sustained very low body fat in women is associated with menstrual disruption and reduced bone density.
How the methods compare
| Method | Typical error | Practicality |
|---|---|---|
| DEXA scan | ±1–2% | Clinical, costs money, gold standard |
| Hydrostatic weighing | ±2–3% | Lab only, requires full submersion |
| Bod Pod | ±2–3% | Lab only |
| Skinfold calipers | ±3–4% | Cheap, very dependent on the operator |
| US Navy tape method | ±3–4% | Free, repeatable at home |
| Bioelectrical impedance scales | ±4–8% | Easy, badly affected by hydration |
| BMI-derived formula | ±5–8% | Needs no measuring, least reliable |
Consumer impedance scales swing with hydration, food and time of day. A reading can move three points between morning and evening without any change in body composition. If you use one, always measure at the same time under the same conditions and watch the trend rather than any single figure.
Lean body mass
Lean mass is total weight minus fat mass, and it is often the more useful number to track during weight loss. Someone at 90 kg and 28% fat carries 25.2 kg of fat and 64.8 kg of lean mass. If they drop to 82 kg at 22%, they now have 18 kg of fat and 64 kg of lean, meaning almost all of the 8 kg lost was fat. If instead they reached 82 kg at 25%, they would have lost 4.7 kg of fat and 3.3 kg of lean tissue, which is a far worse outcome from the same scale reading.
A worked example
A woman of 168 cm with a 74 cm waist, 97 cm hips and a 32 cm neck gets an estimated 26.4% body fat by the Navy method, which falls in the average band. At 64 kg that is 16.9 kg of fat and 47.1 kg of lean mass. Tracking those two figures over a training block tells her far more than the scale alone.
This page explains published formulas and population-level ranges. It is general information, not medical advice, and it cannot account for your individual health. Talk to a doctor or a registered dietitian before changing how you eat, train or treat a condition.
Frequently Asked Questions (FAQs)
What is a healthy body fat percentage?
For men, roughly 14% to 24% covers fitness through average. For women, 21% to 31%. Below the essential threshold of about 5% for men and 13% for women, normal physiological function is compromised. Very low body fat is a performance state athletes hold briefly, not a year-round target.
How accurate is the Navy tape method?
Within about three to four percentage points of a DEXA scan for people of typical build. It is less reliable at the extremes and for people carrying unusual fat distribution. Its real strength is consistency: measured the same way each time, it tracks change well even if the absolute number is slightly off.
Why do body fat scales give such different readings?
They pass a small current through the body and infer composition from the resistance, which depends heavily on hydration. Drinking a litre of water, eating a meal or exercising beforehand can shift the reading by several points. Measure at the same time of day, before eating or drinking, for any consistency at all.
Can I lose fat without losing weight?
Yes, and it is common when starting resistance training. Gaining muscle while losing fat can leave the scale almost unchanged while your composition and measurements improve substantially. This is exactly the situation where tracking body fat rather than weight pays off.
How fast can I safely reduce body fat?
Around 0.5% to 1% of body weight per week is a common guideline. Faster loss increasingly comes from muscle rather than fat, and the steeper the deficit the more of it is lean tissue. Resistance training and adequate protein, typically 1.6 to 2.2 g per kg of body weight, substantially reduce that loss.
Does spot reduction work?
No. Training a muscle does not preferentially burn the fat sitting on top of it. Fat is mobilised from across the body in a pattern largely determined by genetics and hormones. Abdominal exercises build abdominal muscle; they do not remove abdominal fat.