# Gray (unit)

Gray (symbol Gy) is the SI unit for absorbed dose.

## Definition

One gray is one joule of radiation energy absorbed by one kilogram of matter.
One
G
y
One
J
k
g
One
m
2
⋅
s
−
2
{\displaystyle 1\ \mathrm {Gy} 1\ {\frac {\mathrm {J} }{\mathrm {kg} }}1\ \mathrm {m} ^{2}\cdot \mathrm {s} ^{-2}}
It is the same unit as the sievert. In order to avoid the risk of confusion of absorbed dose and dose, gray should be used for absorbed radiation and sievert should be used for dose.

## Origin

Gray was defined in 1975 after Louis Harold Gray (1905-1965).

## Transform

1 gray equals 100 rad 1 hectorad.