Your scale is not wrong.
It is just answering a different question.
It tells you what you weigh. It cannot tell you what that weight is made of, or where it sits — and that is the part that says something.
Four ways to look at a body
Each of these does something the others do not. The question is not which is best but which answers your question.
| ScaleAt home | Bio-impedanceSmart scale, gym | MRIHospital, on referral | DEXAHere, 45 minutes | |
|---|---|---|---|---|
| What it measures | Your total weight, in one number. | An estimate of the fat and lean split. | Tissue and structures, in detail and in images. | Fat, muscle and bone, measured separately. |
| Tells fat from muscle | No. A kilo is a kilo. | Estimated, not measured. | Yes, from the images. | Yes, as separate values. |
| Says where the fat sits | No. | Barely — usually one figure for the whole body. | Yes, and in the most detail of the four. | Yes, per region, including around the organs. |
| Bone density | No. | No. | Not what it is for. | Yes — this is the measurement hospitals use for it. |
| Affected by what you drank or ate | Yes, noticeably. | Yes — it measures how easily a current passes, and that shifts with hydration. | No. | No. |
| Radiation | None. | None; it uses a small current. | None; it uses a magnetic field. | A very low X-ray dose. It is why a physician reviews every request. |
| What it is for | Following a trend day to day. | A rough indication, cheap and quick. | Diagnosis, when something specific needs looking at. | A baseline you can measure against later. |
This table compares what each method measures and does not measure. It deliberately avoids figures for dose, accuracy and price: those need a source, and the sources for this page have not been supplied yet. Once they are, the numbers go in here with the reference beside them.
What this does not replace
A DEXA scan is not a health check and not a diagnosis. It says nothing about your heart, your blood or your hormones, and it does not look for disease. If that is your question, a doctor is the right address and this scan is not.
What it does is measure, precisely and repeatably, what your body is made of. That is a narrow thing to be good at, and it is the thing we are good at.