Dose visualizer
Radiation dose, in context
Everyone on Earth lives in a bath of natural background radiation from soil, food, buildings and the sky: about 3 millisieverts (mSv) every year. The most useful way to understand a medical exam's dose is to place it on that same scale.
Most X-rays sit at hours-to-days of background. CT uses more, which is exactly why doctors order it only when the answer is worth it. MRI and ultrasound use none at all.
Chest X-ray
0.1 mSv
Approximate effective dose
about 12 days
of natural background radiation
The most common X-ray of all.
Population average for a typical adult exam; the dose for any one person and machine differs. MRI and ultrasound sit at zero on this scale: they use no ionising radiation.
The full reference table
| Examination | Approx. dose | Natural background equivalent |
|---|---|---|
| Hand or foot X-ray | 0.001 mSv | about 3 hours |
| Dental bitewing X-ray | 0.005 mSv | about 15 hours |
| Chest X-ray | 0.1 mSv | about 12 days |
| Mammogram (both breasts) | 0.4 mSv | about 49 days |
| Lower back (lumbar spine) X-ray | 1.4 mSv | about 6 months |
| Head CT | 2 mSv | about 8 months |
| Chest CT | 7 mSv | about 2.3 years |
| Abdomen and pelvis CT | 10 mSv | about 3 years |
| Coronary CT angiogram | 12 mSv | about 4 years |
| MRI and ultrasound | 0 mSv | No ionising radiation at all |
Values follow the RadiologyInfo.org adult dose table and are rounded population averages. Children's protocols are specifically adjusted downward; always mention a known or possible pregnancy before any X-ray or CT examination.
Sources
- Radiation dose to adults from common imaging examinations RadiologyInfo.org (ACR / RSNA), 2024Source of the approximate effective doses and background-time comparisons, using about 3 mSv per year of natural background.
- Sources and effects of ionizing radiation (world-average background about 2.4 mSv per year) UNSCEAR, United Nations, 2020
- Ionizing radiation and health effects World Health Organization, 2023
Last reviewed: 2026-07-16