What is the formula for converting rem to rad?

Rad = Rem ÷ Q, where Q is the dimensionless quality factor of the radiation type. For gamma, X-ray, and beta radiation Q = 1, so rad = rem. For alpha particles Q = 20, so 1 rem = 0.05 rad.

What is a quality factor (Q)?

Quality factor (Q) is a 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, so Rad = Rem ÷ Q.

When is 1 rem equal to 1 rad?

Only when the quality factor Q = 1, which applies to gamma rays, X-rays, and beta particles. For all other radiation types with Q > 1, one rem corresponds to fewer than one rad.

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 does converting rem to rad matter?

Dose equivalent (rem) weights absorbed dose by biological effectiveness, useful for regulatory limits. Absorbed dose (rad) is the physical energy deposit, needed for calculating tissue heating, material activation, or comparing measurements from instruments that report in rad.

Rem to Rad Converter

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

Convert dose equivalent (rem) to absorbed dose (rad) for any radiation type using the appropriate quality factor.

Input

Dose Equivalent

Radiation Type

Result

Enter a dose and click Convert.

Quality Factors Reference (ICRP 26)

Radiation Type	Q	1 rem =	Example
Gamma rays	1	1 rad	Co-60, Cs-137
X-rays	1	1 rad	Diagnostic imaging
Beta particles	1	1 rad	H-3, C-14, Sr-90
Thermal neutrons	5	0.2 rad	Reactor environments
Fast neutrons (~0.1–2 MeV)	10	0.1 rad	Nuclear reactors, cosmic rays
Protons	10	0.1 rad	Proton therapy, cosmic rays
Alpha particles	20	0.05 rad	Radon-222, Po-210
Fission fragments	20	0.05 rad	Nuclear fission products

Summary

Convert dose equivalent (rem) to absorbed dose (rad) for any radiation type using the appropriate quality factor.

How it works

Enter the dose equivalent in rem in the input field.
Select the radiation type or enter a custom quality factor (Q).
The converter divides rem by Q to produce the absorbed dose in rad.
Results update on click; secondary outputs show millirad, gray, and milligray equivalents.
Switch between rem and mrem inputs using the unit toggle.

Use cases

Radiation safety officers back-calculating absorbed dose from recorded dose equivalent readings.
Health physics students learning the inverse relationship between rem and rad.
Nuclear medicine professionals converting dose equivalent measurements to absorbed dose.
Industrial radiographers checking absorbed dose limits from rem-based dosimeter records.
Researchers converting rem-reported data to rad for older literature comparisons.
Emergency responders estimating absorbed dose from dose equivalent field readings.

Frequently Asked Questions

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