Gray to Rad Converter (Gy ⇄ rad)
Convert radiation absorbed dose between gray (Gy) and rad instantly, with precise formulas, examples, and a quick reference table.
Gray ⇄ Rad Online Calculator
SI unit of absorbed dose. 1 Gy = 1 J/kg.
Legacy unit. 1 rad = 0.01 Gy.
Conversion factors
- 1 gray (Gy) = 100 rad
- 1 rad = 0.01 gray (Gy)
Quick gray to rad reference table
| Gray (Gy) | Rad |
|---|---|
| 0.01 Gy | 1 rad |
| 0.1 Gy | 10 rad |
| 0.5 Gy | 50 rad |
| 1 Gy | 100 rad |
| 2 Gy | 200 rad |
| 5 Gy | 500 rad |
| 10 Gy | 1,000 rad |
How to convert gray to rad
Gray (symbol: Gy) is the SI unit of absorbed dose, while rad is an older, non-SI unit. They measure the same physical quantity: the amount of ionizing radiation energy absorbed per unit mass.
Exact relationship
\(1 \text{ Gy} = 100 \text{ rad}\)
\(1 \text{ rad} = 0.01 \text{ Gy}\)
Formula: gray to rad
To convert an absorbed dose from gray to rad, multiply by 100:
\[ D_{\text{rad}} = D_{\text{Gy}} \times 100 \]
Example
A patient receives a dose of 2.5 Gy. What is this in rad?
\[ D_{\text{rad}} = 2.5 \times 100 = 250 \text{ rad} \]
Formula: rad to gray
To convert an absorbed dose from rad to gray, divide by 100 (or multiply by 0.01):
\[ D_{\text{Gy}} = \frac{D_{\text{rad}}}{100} = D_{\text{rad}} \times 0.01 \]
Example
A legacy report lists a dose of 75 rad. What is this in gray?
\[ D_{\text{Gy}} = \frac{75}{100} = 0.75 \text{ Gy} \]
What are gray and rad?
Gray (Gy)
The gray is the SI unit of absorbed dose and is defined as:
\[ 1 \text{ Gy} = 1 \frac{\text{joule}}{\text{kilogram}} = 1 \text{ J/kg} \]
It is widely used in radiation therapy, radiobiology, and radiation protection to quantify how much energy ionizing radiation deposits in tissue or other materials.
Rad
The rad (radiation absorbed dose) is an older CGS unit of absorbed dose. It is defined as:
\[ 1 \text{ rad} = 0.01 \text{ J/kg} = 0.01 \text{ Gy} \]
Although the gray has officially replaced the rad in the SI system, rad is still encountered in older literature, some regulatory documents, and on legacy equipment, which is why a reliable converter is useful.
Typical dose ranges (order of magnitude)
Approximate absorbed dose levels, expressed in both units:
- Diagnostic X‑ray (single image): ~0.001–0.01 Gy (0.1–1 rad)
- CT scan (whole body): ~0.01–0.03 Gy (1–3 rad)
- Radiation therapy (single fraction): ~1–3 Gy (100–300 rad)
- Radiation therapy (full course): ~50–70 Gy (5,000–7,000 rad)
These are broad, illustrative ranges only. Actual clinical doses depend on the specific protocol, equipment, and patient characteristics.
Gray vs. rad vs. sievert
Gray and rad both describe absorbed dose (energy per unit mass). They do not directly account for the biological effect of different types of radiation.
- Gray (Gy) / rad: physical absorbed dose (J/kg).
- Sievert (Sv) / rem: equivalent or effective dose, which includes radiation weighting factors and tissue weighting factors to reflect biological risk.
For many medical X‑ray and gamma‑ray applications, numerical values in Gy and Sv can be similar, but they represent different concepts and should not be interchanged without proper context.
FAQ
How precise is this gray to rad converter?
The converter uses the exact definition 1 Gy = 100 rad and performs calculations in double‑precision floating point. Results are shown with up to a reasonable number of decimal places depending on your input.
Can I enter very small or very large values?
Yes. You can enter values in scientific notation (for example,
1e-3 for 0.001 Gy or 2.5e3 for 2500
Gy) and the calculator will handle them correctly, subject to
normal browser number limits.
Is this tool suitable for clinical decision-making?
This converter is intended for educational and general reference purposes only. It should not be used as the sole basis for clinical, safety, or regulatory decisions. Always follow local protocols and consult qualified medical physics or radiation safety professionals.