Absorbed Dose Converter
Absorbed dose is the energy deposited by ionizing radiation per unit mass, with the SI unit of the gray (Gy), equal to one joule per kilogram. The older CGS unit is the rad, where 100 rad equals 1 gray. This converter moves a dose between gray, milligray, rad, kilorad, joule per kilogram, and erg per gram, using exact definitions: 1 Gy equals 1 J/kg, 1 rad equals 0.01 Gy, and 1 erg/g equals 1e-4 Gy. It covers absorbed dose only, not equivalent dose (sieverts) or activity (becquerels).
Absorbed dose conversion
Base value (Gy) = input * factor(from unit)
Output = base value / factor(to unit)
1 Gy = 1 J/kg
1 rad = 0.01 Gy
1 erg/g = 1e-4 Gy
The gray and the joule per kilogram are identical by definition. The rad is the CGS unit: 100 rad equals 1 gray.
Absorbed dose context
- The SI unit of absorbed dose is the gray (Gy), defined as one joule per kilogram.
- The older rad is exactly 0.01 gray, so 100 rad equals 1 Gy.
- Absorbed dose differs from equivalent dose (sievert), which weights for radiation type.
- 1 erg per gram equals 1e-4 gray, since 1 erg is 1e-7 J and 1 g is 1e-3 kg.
- Medical and industrial doses are commonly quoted in gray or milligray.
Absorbed dose: frequently asked questions
What is the difference between gray and sievert?
The gray measures absorbed dose, the physical energy deposited per kilogram. The sievert measures equivalent or effective dose, which multiplies the gray by weighting factors for the radiation type and tissue sensitivity. This converter handles absorbed dose (gray) only.
How many rad are in a gray?
One hundred. The rad is defined as 0.01 gray, so 1 Gy equals 100 rad and 1 mGy equals 0.1 rad.
Is a gray the same as a joule per kilogram?
Yes, exactly. The gray is defined as one joule of energy absorbed per kilogram of matter, so the two units are interchangeable.
How do I convert erg/g to gray?
One erg is 1e-7 joule and one gram is 1e-3 kilogram, so 1 erg/g equals 1e-7 J over 1e-3 kg, which is 1e-4 J/kg, or 1e-4 gray.
Does this convert radiation activity?
No. Activity (becquerel or curie) measures the rate of nuclear decays, a different quantity. This tool converts absorbed dose only.
Official sources
- NIST Special Publication 811: Guide for the Use of the International System of Units.
- BIPM: SI Units.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.