How much radiation is that?
Radiation doses span seven orders of magnitude and almost every one people encounter is at the harmless end.
50% of a head CT scan
1 mSv is more than 5 of the 11 references on this page.
Reference figures are measurements and are rounded; the unit conversion behind them is exact.
| Reference | Size | Yours ÷ theirs | Note |
|---|---|---|---|
| eating a banana | 0.0001 mSv | 10,000× | 0.1 µSv |
| a dental X-ray | 0.005 mSv | 200× | |
| a transatlantic flight | 0.04 mSv | 25× | |
| a chest X-ray | 0.1 mSv | 10× | |
| a mammogram | 0.4 mSv | 2.5× | |
| a head CT scan | 2 mSv | 0.5× | |
| annual background dose | 2.4 mSv | 0.417× | |
| a chest CT scan | 7 mSv | 0.143× | |
| annual limit for workers | 20 mSv | 1/20 | |
| first symptoms of sickness | 1,000 mSv | 1/1,000 | |
| usually fatal without treatment | 5,000 mSv | 1/5,000 |
Worth knowing
- A banana delivers about 0.1 microsieverts from its potassium-40 — roughly a ten-millionth of the dose that causes any symptoms.
- Natural background radiation gives everyone about 2.4 mSv a year, more than a chest CT scan.
Frequently asked
Is flying dangerous because of radiation?
Not for passengers. A transatlantic flight is about 40 µSv, or 1.6% of a year’s background dose. Frequent aircrew are monitored as radiation workers.
What is a sievert?
A measure of biological effect, not raw energy — it weights absorbed dose by how damaging the radiation type is. One sievert is a very large dose; everyday exposures are in microsieverts.
How to read this
Doses are representative; actual values vary with equipment, technique and location.