Rad is 0.01 gray.
Rads to Grays Converter — rad to Gy
Convert Rad (rad) to Gray (Gy) using the exact conversion factor (1 rad = 0.01 gray). See the formula, worked examples, conversion table, unit comparison, history, and common uses.
Rads to Grays 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.
Gray is absorbed dose in joules per kilogram.
Result = input x 0.01 / 1.
Absorbed Dose units are compatible.
Reserved above the conversion cards and below the converter.
About Converting Rads to Grays
Rad and Gray 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. Rad is typically associated with still used in some US medical and historical contexts alongside the SI gray, while Gray is typically associated with universal — SI derived unit used worldwide in medicine and radiation protection.
Formula
grays = rads × 0.01
This factor comes from each unit's defined relationship to the category's base unit: 1 rad equals 0.01 base units, and 1 gray equals 1 base unit, so dividing one by the other gives the direct rad-to-gray factor of 0.01.
Simple example
1 rad × 0.01 = 0.01 Gy
1 rad = 0.01 grays.
Real-world example
10 rad × 0.01 = 0.1 Gy
10 rads = 0.1 grays.
Conversion table
| Rad (rad) | Gray (Gy) |
|---|---|
| 0.001 rad | 0.00001 Gy |
| 0.01 rad | 0.0001 Gy |
| 0.1 rad | 0.001 Gy |
| 1 rad | 0.01 Gy |
| 10 rad | 0.1 Gy |
| 100 rad | 1 Gy |
Reverse conversion: Gray to Rad
0.01 Gy × 100 = 1 rad
0.01 grays = 1 rad.
rads = grays × 100
For a page dedicated to this direction, see Gray to Rad.
Rad vs. Gray
| Aspect | Rad | Gray |
|---|---|---|
| Family | non-SI unit, still common in the US | SI derived unit |
| Typical use | US radiation therapy dose records (historically) | Radiation therapy dose prescriptions in medicine |
| Where it's used | Still used in some US medical and historical contexts alongside the SI gray | Universal — SI derived unit used worldwide in medicine and radiation protection |
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
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.
Rad — sources
- NIST Guide to the SI, Appendix B — Lists the rad among non-SI units with an exact SI equivalence.
Gray — sources
- BIPM SI Brochure, 9th edition — Official definition of the gray as an SI derived unit.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many grays are in 1 rad?
1 rad equals 0.01 grays, using the exact defined conversion factor rather than an estimate.
How do I convert rad to gray?
Multiply the rad value by 0.01. The converter above does this instantly to whatever precision you set.
How do I convert gray back to rad?
Use the reverse factor: 1 gray equals 100 rads. You can also use the swap control in the converter above to flip the direction instantly.
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.
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.
Is the rad to gray 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 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.
Where is the rad still used today?
Still used in some US medical and historical contexts alongside the SI gray