How to measure body fat: 6 methods compared
From hospital scanners to a tape measure: how far off each method is, what it costs and which one to use to track your progress.
Updated November 3, 2026 · 7 min read
There's no perfect way to measure body fat outside a lab. Every method is an estimate with its own margin of error. The good news: to see your progress you don't need the most accurate one, but one you can repeat the same way every time.
1. DEXA
Dual-energy X-ray absorptiometry is the reference in clinics and research. It separates fat, muscle and bone by body region with an error of about ±1–2 points. The downside: it costs money, you have to go to a clinic and it isn't practical to repeat every month.
2. Bioimpedance (smart scales)
It sends a very weak current through your body and estimates fat from the resistance. It's convenient and cheap, but very sensitive to hydration: drinking, sweating or eating changes the result by several points. Home scales are the least accurate; professional multi-electrode devices are considerably better.
3. Calipers (skinfolds)
A caliper measures the thickness of fat under the skin at several points. In expert hands it's fairly reliable (±3–4 points), but it depends heavily on who measures and doesn't capture visceral fat.
4. Navy method (tape measure)
It estimates fat from your neck, waist and, for women, hip circumferences. It's free, quick and surprisingly useful for tracking trends if you always measure the same way. You can try it with our body fat calculator.
5. AI photo analysis
Computer vision models estimate fat from a photo, like an experienced coach would, but without the subjectivity. Their big advantage is that, besides the number, they see where fat is stored and how developed your muscles are. To stay consistent, photos should always be taken with the same lighting, clothing and pose.
6. The mirror (and progress photos)
It doesn't give a number, but photos taken under the same conditions every few weeks are one of the best ways to see real changes the scale doesn't show.
Quick comparison
| Method | Accuracy | Cost | For tracking progress |
|---|---|---|---|
| DEXA | Very high | High | Not practical |
| Bioimpedance | Variable | Low – medium | If you control hydration |
| Calipers | High (if done well) | Low | With the same person measuring |
| Navy method | Medium | Free | Yes |
| AI photo | Medium – high | Low | Yes, and you see where you change |
| Mirror and photos | No number | Free | Yes |
Which one to choose
If you want an exact reference number, get a DEXA scan now and then. Day to day, combine a repeatable method (the tape or photo analysis) with progress photos every two to four weeks. What matters is the trend, not a single measurement.
Frequently asked questions
Outside a lab, DEXA, with an error of around ±1–2 points.
They're useful for spotting trends if you always weigh in under the same conditions, but the number can vary by several points depending on hydration.
Yes, as an estimate. AI models analyze the shape and definition of the body; they work best with photos always taken under the same conditions.
Keep reading
- Body fat calculator (US Navy method)A tape measure and two minutes: your estimated body fat percentage using the formula the United States Navy uses.
- Ideal body fat percentage: charts for men and womenWhat body fat percentage is healthy, what counts as athletic and why your ideal number depends on your sex and your goals.
- BMI calculator (body mass index)Your body mass index in seconds, what it means according to the WHO and, above all, what BMI can't tell you.