Radiation-Absorbed Dose Converter
Convert absorbed radiation dose, the energy absorbed per unit of mass, between gray, centigray, milligray, rad, millirad and joule per kilogram, gram, centigram or milligram. Pick two units, enter a value and read the result instantly.
Select two units to see the conversion factor.
Absorbed dose is energy per mass. It is not equivalent or effective dose (sievert, rem), and this tool does not convert gray into sievert. This is a unit converter, not a safety or medical assessment.
Absorbed Dose Formula
Every absorbed dose unit is a fixed multiple of one reference unit, the gray (1 Gy = 1 J/kg). To convert, multiply the value by the size of the source unit in Gy, then divide by the size of the target unit in Gy. The relationships are exact: 1 rad = 0.01 Gy, 1 J/g = 1,000 Gy, 1 J/cg = 100,000 Gy, 1 J/mg = 1,000,000 Gy, and each SI prefix is a power of ten.
What Is Absorbed Dose?
Absorbed dose is the energy that ionizing radiation deposits in a material, divided by the mass of that material: D = energy ÷ mass. The SI unit is the gray (Gy), defined as one joule of absorbed energy per kilogram, which is why joule per kilogram appears in the list as an identical unit. The gray applies to any material, such as tissue, air, water or a plastic, and to any kind of ionizing radiation.
The older CGS unit is the rad, which is 100 erg of absorbed energy per gram and equals 0.01 Gy. Hence 1 Gy = 100 rad, and the centigray (cGy) equals exactly one rad. Medical physics often uses the centigray for this reason. Other units in the list are simply joules per different masses: 1 J/g equals 1,000 Gy, 1 J/cg 100,000 Gy and 1 J/mg 1,000,000 Gy.
Absorbed dose is not the same as equivalent or effective dose. Equivalent dose, in sievert (Sv), multiplies the absorbed dose by a radiation weighting factor (1 for X-rays, gamma rays and electrons, about 20 for alpha particles, and different values for neutrons and protons). Effective dose then weights the results by tissue sensitivity. Because the sievert depends on the radiation type and tissue, gray and sievert are not interchangeable in every situation, and a value in Gy should never be read as Sv without that information. Equivalently, 1 rem = 0.01 Sv is the older unit of equivalent dose, not of absorbed dose.
Absorbed dose also differs from activity (becquerel, curie), which counts decays in a source, and from exposure (roentgen, C/kg), which measures ionization in air from X-rays and gamma rays. Neither can be converted directly into absorbed dose without additional information about the radiation and the material.
Supported Units
This converter supports the following 23 absorbed dose units: rad and millirad, joule per kilogram, gram, centigram and milligram, and gray with every SI prefix from exa to atto. The last column shows how many gray one unit equals.
| Unit | Symbol | Value in Gy |
|---|---|---|
| Rad | rad | 0.01 |
| Millirad | mrad | 1e-5 |
| Joule per kilogram | J/kg | 1 |
| Joule per gram | J/g | 1,000 |
| Joule per centigram | J/cg | 100,000 |
| Joule per milligram | J/mg | 1,000,000 |
| Gray | Gy | 1 |
| Exagray | EGy | 1e+18 |
| Petagray | PGy | 1e+15 |
| Teragray | TGy | 1e+12 |
| Gigagray | GGy | 1,000,000,000 |
| Megagray | MGy | 1,000,000 |
| Kilogray | kGy | 1,000 |
| Hectogray | hGy | 100 |
| Dekagray | daGy | 10 |
| Decigray | dGy | 0.1 |
| Centigray | cGy | 0.01 |
| Milligray | mGy | 0.001 |
| Microgray | µGy | 1e-6 |
| Nanogray | nGy | 1e-9 |
| Picogray | pGy | 1e-12 |
| Femtogray | fGy | 1e-15 |
| Attogray | aGy | 1e-18 |
How to Use the Radiation-Absorbed Dose Converter
- Type the absorbed dose in the value box. Decimals and scientific notation such as 0.0025 or 2.5e-3 are accepted.
- Choose the From unit and the To unit.
- The result appears instantly, or press Convert Now. Very large or very small results are shown in scientific notation.
- Use Swap Units to reverse the conversion, Copy Result to copy the answer, open Show this value in all units for a full list, and Clear to start again.
Step-by-step by hand
- Find the size of each unit in the common base unit (Gy): 1 rad = 0.01 Gy and 1 Gy = 1 Gy.
- Divide the source size by the target size to get the conversion factor: 0.01 ÷ 1 = 0.01, so 1 rad = 0.01 Gy.
- Multiply by your value: 200 rad × 0.01 = 2 Gy.
Absorbed dose cannot be negative, so only zero and positive numbers are accepted.
Common Absorbed Dose Conversions
- Radiotherapy fraction: 2 Gy equals 200 cGy, which is 200 rad.
- Old to new units: 200 rad equals 2 Gy.
- Imaging-scale doses: 5 mGy equals 0.5 rad and 500 mrad.
- Very small doses: 250 µGy equals 0.25 mGy or 25 mrad.
- Industrial irradiation: 25 kGy equals 25,000 Gy or 0.025 MGy.
- Energy per mass: 0.004 J/g equals 4 Gy.
- Joule per kilogram: 3 J/kg equals 3 Gy, exactly the same quantity.
Rad to Gray Conversion – Common Values
Quick reference for frequently used values
| Rad | Gray (Gy) | Centigray (cGy) | Milligray (mGy) | Joule/gram |
|---|---|---|---|---|
| 0.001 | 1e-5 | 0.001 | 0.01 | 1e-8 |
| 0.01 | 0.0001 | 0.01 | 0.1 | 1e-7 |
| 0.1 | 0.001 | 0.1 | 1 | 1e-6 |
| 1 | 0.01 | 1 | 10 | 1e-5 |
| 5 | 0.05 | 5 | 50 | 5e-5 |
| 10 | 0.1 | 10 | 100 | 0.0001 |
| 50 | 0.5 | 50 | 500 | 0.0005 |
| 100 | 1 | 100 | 1,000 | 0.001 |
| 200 | 2 | 200 | 2,000 | 0.002 |
| 1,000 | 10 | 1,000 | 10,000 | 0.01 |
Where and Why This Conversion Is Used
- Radiotherapy and medical physics: prescriptions and treatment-plan doses are written in Gy or cGy, and older records use rad.
- Diagnostic imaging: dose indicators and reference levels are given in mGy.
- Radiation protection: older regulations, textbooks and dosimeters use rad and millirad.
- Industrial processing: radiation sterilization and food or polymer irradiation are specified in kGy.
- Radiobiology and research: experiments compare doses from sources calibrated in different units.
Important Differences Between Related Radiation Measurements
- Absorbed dose (Gy, rad): energy absorbed per kilogram of a material.
- Equivalent dose (Sv, rem): absorbed dose multiplied by a radiation weighting factor.
- Effective dose (Sv): a tissue-weighted sum of equivalent doses over the body.
- Exposure (R, C/kg): ionization in air from X-rays and gamma rays.
- Activity (Bq, Ci): decays per second in a source.
See the Radiation Converter for dose rates, the Radiation-Exposure Converter for roentgen and the Radiation-Activity Converter for becquerel and curie.
Educational disclaimer: this page converts units of measurement only. The results are not a radiation-safety assessment, a dose estimate for a person or a medical opinion, and they should not replace advice from a qualified radiation-safety officer, medical physicist or physician.