Gray is absorbed dose in joules per kilogram.
Grays to Zeptograys Converter — Gy to zGy
Convert Gray (Gy) to Zeptogray (zGy) using the exact conversion factor (1 gray = 1e+21 zeptogray). See the formula, worked examples, conversion table, history, and common uses.
Grays to Zeptograys 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.
Zeptogray is 1e-21 gray units.
Result = input x 1 / 1e-21.
Absorbed Dose units are compatible.
Reserved above the conversion cards and below the converter.
About Converting Grays to Zeptograys
Gray and Zeptogray 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 most often used for radiation therapy dose prescriptions in medicine.
Formula
zeptograys = grays × 1e+21
This factor comes from each unit's defined relationship to the category's base unit: 1 gray equals 1 base unit, and 1 zeptogray equals 1e-21 base units, so dividing one by the other gives the direct gray-to-zeptogray factor of 1e+21.
Simple example
1 Gy × 1e+21 = 1e+21 zGy
1 gray = 1e+21 zeptograys.
Real-world example
10 Gy × 1e+21 = 1e+22 zGy
10 grays = 1e+22 zeptograys.
Conversion table
| Gray (Gy) | Zeptogray (zGy) |
|---|---|
| 0.001 Gy | 1e+18 zGy |
| 0.01 Gy | 1e+19 zGy |
| 0.1 Gy | 1e+20 zGy |
| 1 Gy | 1e+21 zGy |
| 10 Gy | 1e+22 zGy |
| 100 Gy | 1e+23 zGy |
Reverse conversion: Zeptogray to Gray
1e+21 zGy × 1e-21 = 1 Gy
1e+21 zeptograys = 1 grays.
grays = zeptograys × 1e-21
For a page dedicated to this direction, see Zeptogray to 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 Zeptogray (zGy)
Zeptogray is 1e-21 gray units.
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 zeptograys are in 1 gray?
1 gray equals 1e+21 zeptograys, using the exact defined conversion factor rather than an estimate.
How do I convert gray to zeptogray?
Multiply the gray value by 1e+21. The converter above does this instantly to whatever precision you set.
How do I convert zeptogray back to gray?
Use the reverse factor: 1 zeptogray equals 1e-21 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 zeptogray?
Zeptogray (zGy) is a unit of radiation.
Is the gray to zeptogray conversion exact?
Yes. Both gray and zeptogray are defined by fixed standards rather than physical artifacts, so the factor of 1e+21 used above is exact to as many digits as you choose to display.
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