This absorbed dose converter changes radiation dose between grays, milligrays, micrograys, centigrays, rads and millirads. The gray is one joule of energy absorbed per kilogram. The absorbed dose conversion factor to the older unit is exact: 1 rad = 0.01 Gy = 1 cGy, so 1 Gy = 100 rad.
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How to use the absorbed dose converter
- Enter the dose, for example 2 Gy.
- In the absorbed dose converter, choose its unit and the target unit, such as Gy to rad.
- Read the absorbed dose converter result: 2 Gy = 200 rad.
For Gy to rad, multiply by 100. For rad to Gy, divide by 100. The rad and the cGy are the same size.
What is absorbed radiation dose?
Absorbed dose is the energy deposited by ionizing radiation per unit mass of material. The SI unit is the gray (Gy), one joule per kilogram; the older unit, the rad, equals 0.01 Gy.
Conversion formula
The absorbed dose converter stores every unit as a multiple of the base unit, the gray (Gy). To convert:
value in target unit = value × (factor of source unit ÷ factor of target unit)
where each factor is the size of the unit in grays.
Common absorbed radiation dose conversions
| From | To | 1 unit equals |
|---|---|---|
| gray (Gy) | rad (rad) | 100 rad |
| rad (rad) | gray (Gy) | 0.01 Gy |
| milligray (mGy) | millirad (mrad) | 100 mrad |
| centigray (cGy) | rad (rad) | 1 rad |
Absorbed dose converter worked example
Convert 25 milligrays to millirad:
- Factor of mGy = 0.001 Gy
- Factor of mrad = 1 × 10−5 Gy
- 25 × 0.001 ÷ 1 × 10−5 = 2,500 mrad
Absorbed radiation dose unit reference
| Unit | Symbol | Group | Equals (Gy) |
|---|---|---|---|
| Gray | Gy | SI | 1 |
| Milligray | mGy | SI | 0.001 |
| Microgray | µGy | SI | 1 × 10−6 |
| Rad | rad | Traditional US | 0.01 |
| Millirad | mrad | Traditional US | 1 × 10−5 |
| Centigray | cGy | SI | 0.01 |
Reverse factors for each absorbed radiation dose unit
The reference table gives each unit in grays. To go the other way, divide by that factor; the list below does the division for you.
- Milligray (mGy), SI: 1 mGy = 0.001 Gy, so 1 Gy = 1,000 mGy.
- Microgray (µGy), SI: 1 µGy = 1 × 10−6 Gy, so 1 Gy = 1,000,000 µGy.
- Rad (rad), Traditional US: 1 rad = 0.01 Gy, so 1 Gy = 100 rad.
- Millirad (mrad), Traditional US: 1 mrad = 1 × 10−5 Gy, so 1 Gy = 100,000 mrad.
- Centigray (cGy), SI: 1 cGy = 0.01 Gy, so 1 Gy = 100 cGy.
From gray to sievert
Absorbed dose measures energy; equivalent dose in sieverts weights it for radiation type. ICRP Publication 103 radiation weighting factors:
| Radiation | Weighting factor w_R | 1 Gy gives |
|---|---|---|
| Photons (X-rays, gamma rays) | 1 | 1 Sv |
| Electrons and muons | 1 | 1 Sv |
| Protons | 2 | 2 Sv |
| Alpha particles and heavy ions | 20 | 20 Sv |
| Neutrons | energy dependent | see ICRP 103 |
So 5 mGy of alpha radiation corresponds to 100 mSv of equivalent dose.
What a gray means physically
1 Gy deposits 1 J in each kilogram, a tiny amount of heat: it would warm water by only about 0.00024 °C. The harm comes from ionization, not heating. In radiotherapy, doses are prescribed in Gy or cGy, often in daily fractions of about 2 Gy. Use the sievert to rem converter for sieverts and rem and the energy unit converter for joules.
Centigray in radiotherapy
Radiotherapy plans are often written in cGy because one centigray equals one rad. A typical fraction is 2 Gy, which is 200 cGy or 200 rad. A course of 30 fractions delivers 60 Gy. The absorbed dose converter moves between Gy, cGy, mGy and rad so old and new records line up.
Absorbed dose measures energy, joules per kilogram. It does not weight radiation type or tissue, which is what the sievert adds.
Very high absorbed doses appear in industry. Food irradiation and medical device sterilization use kilogray levels, often around 25 kGy for sterilizing single-use devices. That is 2.5 million rad. These numbers are for materials and products, not people, and show how wide the range of the unit is, from µGy background readings to kGy process doses.
Related converters and calculators
Related radiation tools:
- Sievert to rem converter: Sv and rem
- Radiation exposure converter: R and C/kg
- Radioactivity converter: Bq and Ci
- Half-life calculator: decay over time
- Energy unit converter: J, kWh, BTU
Sources
BIPM: SI Brochure; NIST Special Publication 811, Appendix B; ICRP Publication 103.
Questions about this calculator
How many rads are in a gray?
100 rad = 1 Gy exactly.
How do I convert Gy to rad?
Multiply by 100. For example, 0.5 Gy = 50 rad.
How do I convert rad to Gy?
Divide by 100. For example, 300 rad = 3 Gy.
Is a cGy the same as a rad?
Yes. 1 cGy = 1 rad = 0.01 Gy.
How do I convert Gy to Sv?
Multiply by the radiation weighting factor: 1 for photons, 20 for alpha particles.
Check the assumptions and units before relying on a result. Financial, tax and health estimates do not replace advice for your individual circumstances.
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