What is the difference between rad and rem?

Rad measures absorbed dose — the energy deposited per unit mass of tissue (1 rad = 0.01 J/kg). Rem (roentgen equivalent man) measures dose equivalent, which weights absorbed dose by the biological effectiveness of the radiation type. For gamma, X-ray, and beta radiation the quality factor Q = 1, so 1 rad = 1 rem. For more ionizing particles like alpha or fast neutrons, Q is higher, so the same absorbed dose causes greater biological harm.

What is a quality factor (Q)?

Quality factor (Q) is a dimensionless multiplier that accounts for the relative biological effectiveness of a radiation type. The ICRP defines Q = 1 for X-ray, gamma, and beta; Q = 5–20 for neutrons depending on energy; Q = 20 for alpha particles and fission fragments. Rem = Rad × Q.

How does rad relate to gray (Gy)?

1 rad equals 0.01 gray (Gy). Gray is the SI unit of absorbed dose; rad is its older CGS equivalent. Similarly, 1 rem equals 0.01 sievert (Sv).

Why is the quality factor for neutrons a range?

Neutron biological effectiveness depends on neutron energy. Thermal (slow) neutrons have Q ≈ 5, while fast neutrons near 0.1–2 MeV can reach Q = 20. This converter uses ICRP 26 reference values; consult your local regulations for precise energy-dependent factors.

Is 1 rad always equal to 1 rem?

Only for gamma rays, X-rays, and beta particles (Q = 1). For alpha particles (Q = 20), 1 rad = 20 rem. For fast neutrons (Q = 10), 1 rad = 10 rem.

Rad to Rem Converter

Name: Rad to Rem Converter
Availability: InStock
Author: Nham Vu

Convert rad to rem for any radiation type by selecting the appropriate quality factor (Q).

Input

Absorbed Dose

Radiation Type

Result

Enter a dose and click Convert.

Quality Factors Reference (ICRP 26)

Radiation Type	Q	Example
Gamma rays	1	Co-60, Cs-137
X-rays	1	Diagnostic imaging
Beta particles	1	H-3, C-14, Sr-90
Thermal neutrons	5	Reactor environments
Fast neutrons (~0.1–2 MeV)	10	Nuclear reactors, cosmic rays
Protons	10	Proton therapy, cosmic rays
Alpha particles	20	Radon-222, Po-210
Fission fragments	20	Nuclear fission products

Summary

Convert rad to rem for any radiation type by selecting the appropriate quality factor (Q).

How it works

Enter the absorbed dose in rad in the input field.
Select the radiation type or enter a custom quality factor (Q).
The converter multiplies rad by Q to produce the dose equivalent in rem.
Results update instantly; use the copy button to grab the value.
Switch between rad and mrad (millirad) inputs using the unit toggle.

Use cases

Radiation safety officers converting absorbed dose measurements to dose equivalents.
Nuclear medicine professionals verifying patient exposure limits.
Health physics students learning the relationship between rad and rem.
Industrial radiographers checking dose records against regulatory limits.
Researchers comparing absorbed dose data reported in rad to rem-based standards.
Emergency responders estimating dose equivalent from field dosimeter readings.

Frequently Asked Questions

Last updated: 2026-07-24 · Reviewed by Nham Vu