Gray is absorbed dose in joules per kilogram.
Grays to Rads Converter — Gy to rad
Convert Gray (Gy) to Rad (rad) using the exact conversion factor (1 gray = 100 rad). See the formula, worked examples, conversion table, unit comparison, history, and common uses.
Grays to Rads converter
Converter
Radiation Converter
Convert radioactivity, absorbed dose, and equivalent dose units by compatible radiation family.
Context values
Some unit families need one extra value for a physically accurate result.
Rad is 0.01 gray.
Result = input x 1 / 0.01.
Absorbed Dose units are compatible.
Reserved above the conversion cards and below the converter.
About Converting Grays to Rads
Gray and Rad both belong to the radiation-measurement family, though radiation quantities fall into genuinely distinct categories: absorbed dose (gray, rad) measures energy deposited in matter, equivalent dose (sievert, rem) weights that for biological harm, and activity (becquerel, curie) measures how often a radioactive source decays — this page only converts between units of the same kind. Gray is typically associated with universal — SI derived unit used worldwide in medicine and radiation protection, while Rad is typically associated with still used in some US medical and historical contexts alongside the SI gray.
Formula
rads = grays × 100
This factor comes from each unit's defined relationship to the category's base unit: 1 gray equals 1 base unit, and 1 rad equals 0.01 base units, so dividing one by the other gives the direct gray-to-rad factor of 100.
Simple example
1 Gy × 100 = 100 rad
1 gray = 100 rads.
Real-world example
10 Gy × 100 = 1,000 rad
10 grays = 1,000 rads.
Conversion table
| Gray (Gy) | Rad (rad) |
|---|---|
| 0.001 Gy | 0.1 rad |
| 0.01 Gy | 1 rad |
| 0.1 Gy | 10 rad |
| 1 Gy | 100 rad |
| 10 Gy | 1,000 rad |
| 100 Gy | 10,000 rad |
Reverse conversion: Rad to Gray
100 rad × 0.01 = 1 Gy
100 rads = 1 gray.
grays = rads × 0.01
For a page dedicated to this direction, see Rad to Gray.
Gray vs. Rad
| Aspect | Gray | Rad |
|---|---|---|
| Family | SI derived unit | non-SI unit, still common in the US |
| Typical use | Radiation therapy dose prescriptions in medicine | US radiation therapy dose records (historically) |
| Where it's used | Universal — SI derived unit used worldwide in medicine and radiation protection | Still used in some US medical and historical contexts alongside the SI gray |
Understanding the Gray
Gray (Gy) measures absorbed radiation dose. The SI derived unit of absorbed radiation dose, equal to one joule of radiation energy absorbed per kilogram of matter. It is classified as a SI derived unit.
Where it's used: Universal — SI derived unit used worldwide in medicine and radiation protection
Gray vs. sievert. The gray measures physically absorbed energy; the sievert measures equivalent dose, which weights the gray value for how biologically damaging a given type of radiation is. The same absorbed dose in gray can correspond to different sievert values depending on the radiation type.
Uses of the Gray today
- Radiation therapy dose prescriptions in medicine
- Radiation safety and occupational dose monitoring
- Nuclear and radiological research
History of the Gray
The gray is named after Louis Harold Gray (1905–1965), a British physicist who pioneered the physics of radiation dosimetry and its biological effects, and was adopted by the CGPM as an SI derived unit in 1975.
Historical origin. Gray was not the invention of a single named person; it developed through the process described above.
Understanding the Rad
Rad (rad) measures absorbed radiation dose. 'Radiation absorbed dose' — the US customary unit of absorbed radiation dose, fixed at exactly 0.01 gray. It is classified as a non-SI unit, still common in the US.
Where it's used: Still used in some US medical and historical contexts alongside the SI gray
Rad vs. gray. Both measure absorbed radiation dose; the gray is the modern SI unit while the rad is the older US customary unit, related by 1 gray = 100 rad exactly.
Uses of the Rad today
- US radiation therapy dose records (historically)
- US nuclear regulatory and medical physics contexts
Gray — sources
- BIPM SI Brochure, 9th edition — Official definition of the gray as an SI derived unit.
Rad — sources
- NIST Guide to the SI, Appendix B — Lists the rad among non-SI units with an exact SI equivalence.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many rads are in 1 gray?
1 gray equals 100 rads, using the exact defined conversion factor rather than an estimate.
How do I convert gray to rad?
Multiply the gray value by 100. The converter above does this instantly to whatever precision you set.
How do I convert rad back to gray?
Use the reverse factor: 1 rad equals 0.01 grays. You can also use the swap control in the converter above to flip the direction instantly.
What is a gray?
Gray (Gy) measures absorbed radiation dose. The SI derived unit of absorbed radiation dose, equal to one joule of radiation energy absorbed per kilogram of matter. It is classified as a SI derived unit.
What is a rad?
Rad (rad) measures absorbed radiation dose. 'Radiation absorbed dose' — the US customary unit of absorbed radiation dose, fixed at exactly 0.01 gray. It is classified as a non-SI unit, still common in the US.
Is the gray to rad conversion exact?
Yes. 'Radiation absorbed dose' — the US customary unit of absorbed radiation dose, fixed at exactly 0.01 gray. That fixed definition is what the converter above uses, so any rounding you see is a display choice, not a limitation of the math.
What is the difference between gray vs. sievert?
The gray measures physically absorbed energy; the sievert measures equivalent dose, which weights the gray value for how biologically damaging a given type of radiation is. The same absorbed dose in gray can correspond to different sievert values depending on the radiation type.
Where is the gray still used today?
Universal — SI derived unit used worldwide in medicine and radiation protection