Why body fat percentage matters more than weight
Two people can weigh exactly the same yet have radically different health profiles. A 80 kg man at 12% body fat carries 9.6 kg of fat and 70.4 kg of lean mass — metabolically healthy. Another 80 kg man at 28% body fat carries 22.4 kg of fat and only 57.6 kg of lean mass — at significantly elevated risk of metabolic disease.
Body fat percentage cuts through the noise of water, muscle, and bone weight to tell you what proportion of your body is actually fat tissue. It is also the correct metric to track during body recomposition, when weight may stay stable while body composition is improving.
Method 1: DEXA scan (most accurate)
Dual-energy X-ray absorptiometry (DEXA) is considered the gold standard for body composition measurement. It uses low-dose X-rays at two different energies to differentiate between fat mass, lean mass, and bone density. Accuracy is within ±1–2% of true body fat.
DEXA scans are available at private clinics, some universities, and sports science facilities, typically costing £50–150 per scan. Ideal for people who want a precise baseline measurement and are willing to pay for it. Annual scans are sufficient for most purposes.
Method 2: Skinfold calipers
Skinfold calipers measure the thickness of subcutaneous fat (fat beneath the skin) at several standardised sites on the body. Common protocols include the 3-site Jackson-Pollock method and the 7-site method used in research settings.
When performed consistently by the same person using the same protocol, calipers are an excellent tracking tool — changes of 1–2mm across sites accurately reflect fat loss or gain. Absolute accuracy is ±3–5% of true body fat, which is good for home use. Calipers are inexpensive (£10–30) and can be used without help if using a single back-of-arm measurement.
Method 3: US Navy circumference method
The Navy Method estimates body fat using body circumference measurements — neck and waist for men, neck, waist, and hips for women — along with height. It requires only a tape measure and is highly reproducible.
Men formula:
% BF = 86.010 × log10(abdomen − neck) − 70.041 × log10(height) + 36.76
Women formula:
% BF = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387
Accuracy is ±3–4% of true body fat — comparable to calipers and suitable for tracking changes over time. Our Body Fat Calculator uses this method.
Method 4: Bioelectrical impedance (BIA scales)
BIA scales send a small electrical current through the body and estimate body fat based on the resistance of different tissues (fat resists current more than muscle). They are convenient and inexpensive, but accuracy is highly sensitive to hydration status.
Testing after exercise (when dehydrated), after eating, or at different times of day can produce readings that vary by 3–5% between sessions — making them unreliable for tracking. If using BIA, always test in the same conditions: morning, fasted, after using the bathroom.
Healthy body fat ranges
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletic | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average / acceptable | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |