Short answer
InBody and other bioelectrical impedance (BIA) scanners are quick, cheap and very repeatable. They are not interchangeable with DEXA, though. In large studies, BIA read body fat several points lower than DEXA on average, and many individuals sat well outside that average. BIA is weakest at measuring change, which is usually the number people care about. Use one method, keep conditions consistent, and use DEXA when the before and after result matters.
How each method works
| DEXA | BIA (InBody, Evolt, smart scales) | |
|---|---|---|
| What it measures | Low-dose X-ray attenuation, which separates fat, lean soft tissue and bone mineral | Resistance to a small electrical current, converted to body composition by a device model |
| Bone | Measures bone mineral | Doesn't measure bone; estimates it |
| Retest reliability | Very high | Very high |
| Agreement with DEXA | Reference method | Moderate at group level, variable for individuals |
| What moves the reading | Scanner, software, positioning, recent food and fluid | Hydration, recent fluid intake, food, exercise, device model |
| Typical cost | See published fees on our city pages | Often free or low cost at gyms |
What the research found
- Big sample, consistent gap. In 1,000 healthy, active adults, InBody 770 read body fat lower than DEXA by 4.2 percentage points on average in men and 2.8 in women. Both methods were highly repeatable within a week. Visceral fat had the weakest agreement. (European Journal of Clinical Nutrition, 2025)
- Averages hide individuals. In 384 young adults, correlation with DEXA was strong (0.92 to 0.93), but 53% of women and 41% of men were more than 3.5 percentage points away from their DEXA result. (Medicine & Science in Sports & Exercise, 2018)
- Change is the hard part. During a 10-week weight loss programme, BIA and DEXA agreed on average. For individuals, though, the limits of agreement for change in fat mass were about plus or minus 3.7 to 4.6 kg. The authors concluded the two methods can't be used interchangeably for individuals. (NUGENOB, Diabetes & Metabolism, 2011)
- Water moves BIA readings. In 140 adults using foot-to-foot BIA, drinking 500 mL to 2 L of water raised the estimated fat mass by about 2% to 9% compared with baseline, depending on volume and sex. (PMC, 2020)
- DEXA has error too, but it's smaller. On a modern Hologic scanner, the least significant change at 95% confidence was about 2.2% of total fat mass and 1.1% to 1.5% of total lean mass. For someone carrying 20 kg of fat, that's roughly 0.4 kg. (Journal of Medical Imaging and Radiation Oncology, 2017)
- Evolt 360. We did not find an independent, peer-reviewed comparison of Evolt 360 against DEXA when we checked on 20 Oct 2026. Evolt's own FAQ says variation between BIA and DEXA "is anticipated". (Evolt 360 FAQ)
Why your gym scan and your DEXA disagree
- They measure different things. BIA infers fat from water and electrical resistance; DEXA separates tissues by X-ray attenuation.
- Each BIA device uses its own prediction model, so two BIA brands can disagree with each other too.
- Hydration, a recent drink or meal, and training before the scan all shift BIA more than DEXA.
- A different reading on the same day doesn't mean your body changed. Compare like with like: same method, same device, same conditions.
Which to use for a 12 week challenge
- Start and finish: DEXA, on the same scanner, at the same time of day, with the same preparation. The change you're trying to measure is often only a few kilograms, and BIA's individual error for change is about that size.
- Week-to-week check-ins: BIA is fine, as long as conditions are consistent: same device, same time, same hydration, before training.
- Don't compare a BIA number with a DEXA number. Compare each method only with itself.
- Running a gym or team challenge in Sydney? See our Sydney partner.
Preparing for either scan
- Same time of day for every scan, ideally in the morning.
- No training beforehand, and avoid a large meal or drink right before.
- Same clothing, with metal removed.
- For DEXA, follow the clinic's instructions. See how to prepare for a DEXA scan.
Common questions
Is InBody accurate?
It's very repeatable, and reasonable at group level. For individuals, it often reads body fat several points lower than DEXA. In one study of 384 young adults, about half were more than 3.5 points away from DEXA.
Why is my InBody body fat lower than my DEXA?
Large studies found InBody reads lower than DEXA on average, by about 4 points in men and 3 in women. Hydration and the device's prediction model add more variation.
Can I compare my InBody results with my DEXA results?
No. Compare each method only with itself, under the same conditions.
Which is better for tracking a 12 week challenge?
DEXA for the start and finish, because BIA's individual error for change in fat mass is about plus or minus 4 kg. BIA is fine for consistent weekly check-ins.
Do smart scales count as BIA?
Yes. Most home body fat scales use bioimpedance with their own prediction model. Their readings aren't interchangeable with DEXA or with other scales.
Does DEXA have measurement error?
Yes. On modern scanners, a change smaller than about 2% of fat mass or 1% to 1.5% of lean mass can be measurement variation rather than real change.
Checked against the sources linked on this page, 20 Oct 2026. Not medical advice.
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