Gray (Gy) measures absorbed dose — the amount of radiation energy deposited in matter per unit mass (1 Gy = 1 J/kg). Sievert (Sv) measures equivalent dose (or effective dose), which accounts for the biological effect of different types of radiation. For X-rays, gamma rays, and beta particles, the radiation weighting factor wR = 1, so 1 Gy = 1 Sv numerically. For alpha particles (wR = 20), 1 Gy of absorbed dose results in 20 Sv of equivalent dose.

The conversion is straightforward: 1 Gray (Gy) = 100 Rad (rad). To convert Gy to rad, multiply by 100. To convert rad to Gy, divide by 100. This is an exact conversion factor defined by the International Commission on Radiation Units and Measurements (ICRU).

1 Sievert (Sv) = 100 Rem (rem). This is an exact conversion. The rem (roentgen equivalent man) is the traditional CGS unit for equivalent dose, while the sievert is the SI unit. 1 rem = 0.01 Sv, and 1 Sv = 100 rem.

The radiation weighting factor (wR) accounts for the relative biological effectiveness of different radiation types. It is used to convert absorbed dose (Gy) to equivalent dose (Sv): Sv = Gy × wR. The ICRP recommends: wR = 1 for photons (X-rays, gamma) and electrons (beta particles); wR = 2 for protons; wR = 5–20 for neutrons depending on energy; and wR = 20 for alpha particles and fission fragments.

For X-rays and gamma rays, the radiation weighting factor wR equals 1. This means the biological damage per unit of absorbed energy is used as the reference baseline. Since Sv = Gy × wR and wR = 1, the numerical value is the same. However, Gray and Sievert remain distinct quantities — Gray describes physical energy deposition, while Sievert describes biological risk.

The average annual natural background radiation is about 2.4 mSv (240 mrem). The ICRP recommends a limit of 1 mSv/year for the general public (excluding medical and natural background) and 20 mSv/year averaged over 5 years for occupational exposure (with no single year exceeding 50 mSv). Acute doses above 1 Sv (100 rem) may cause radiation sickness, and doses above 4–5 Sv can be lethal without medical intervention.

Not exactly. Rad is the unit of absorbed dose (like Gray), and Rem is the unit of equivalent dose (like Sievert). For X-rays, gamma rays, and beta particles where wR = 1, 1 rad = 1 rem numerically. But for other radiation types like alpha particles (wR = 20), 1 rad of absorbed alpha dose corresponds to 20 rem of equivalent dose. Always check the radiation type when converting between absorbed and equivalent dose units.

This converter uses the exact conversion factors defined by international standards: 1 Gy = 100 rad and 1 Sv = 100 rem (exact). The conversion between absorbed dose (Gy/rad) and equivalent dose (Sv/rem) uses ICRP-recommended radiation weighting factors. For precise radiation protection calculations, especially in mixed radiation fields, consult a qualified health physicist.