Radiation Dose Calculator
Radiation dose from energy deposited in tissue — absorbed dose in gray, effective dose in sievert once the radiation type is weighted — and where it sits against background, a chest X-ray and the occupational limit.
Absorbed dose is energy per kilogram of tissue: one joule per kilogram is one gray.
How the radiation dose calculator works
Absorbed dose is energy per kilogram of tissue: one joule per kilogram is one gray. Effective dose weights that by the radiation type — alpha particles do twenty times the biological damage of gamma rays for the same energy — and the result is in sievert.
The comparisons are what make the number mean anything. Natural background is about 2.4 millisievert a year; a chest X-ray is 0.1; the occupational limit is 20 a year averaged over five.
Formula: D = E / m (Gy); H = D × w_R (Sv)
Worked examples
| Inputs | Effective dose (mSv) | Note |
|---|---|---|
| 0.14 J of gamma in 70 kg | 2 | 2 mSv — most of a year's background |
| The same energy as alpha | 40 | twenty times the effective dose |
| A CT scan's worth | 7 | 7 mSv |
FAQFrequently asked questions
What is the difference between gray and sievert?
Gray measures energy absorbed per kilogram. Sievert weights that for how damaging the radiation type is — the same for X-rays, twenty times more for alpha.
What is a normal dose?
About 2.4 millisievert a year from natural background — rocks, cosmic rays, radon — varying by a factor of several with where you live.
How much is a medical scan?
A chest X-ray about 0.1 mSv; a CT scan 2 to 10; a mammogram 0.4. A single scan is a small fraction of lifetime risk.
What are the limits?
Twenty millisievert a year averaged over five for radiation workers, and one for the public above background. Acute effects begin around a sievert.
Why is alpha weighted twenty?
Because alpha particles deposit their energy in a very short track, doing dense damage. They are harmless outside the body and dangerous inhaled or swallowed.
Where these figures come from
- NIST — CODATA 2018 fundamental physical constants — G, g₀, R, c
- NIST Special Publication 811 — Guide for the use of the International System of Units — unit conversions
- The Engineering ToolBox — material properties — specific heats, expansion coefficients, densities
- National Physical Laboratory — the UK's national measurement institute
Last checked: September 2026. Constants are the CODATA 2018 values; formulas are the standard textbook forms.