What is the weighting factor for X-rays and gamma rays?

The ICRP 103 radiation weighting factor (w_R) for X-rays, gamma rays, and electrons/beta particles is 1. So 1 rad of gamma radiation = 0.01 Sv.

Why does 1 rad of alpha radiation equal 0.20 Sv?

Alpha particles have a w_R of 20 because they deposit energy very densely along a short track, causing far more biological damage per unit of absorbed dose than gamma rays. The higher w_R multiplies the biological harm: 1 rad × 0.01 Gy/rad × 20 = 0.20 Sv.

What is the difference between rad and rem?

Rem (roentgen equivalent man) is the traditional US equivalent-dose unit, analogous to sievert. 1 rem = 0.01 Sv, and 1 rad × w_R = rem numerically. For photons and beta particles, 1 rad = 1 rem = 0.01 Sv. For alpha particles, 1 rad = 20 rem = 0.20 Sv.

Which weighting factor applies to neutrons?

Neutron w_R varies with energy per ICRP 103: it ranges from about 2.5 at thermal energies, peaks near 20 for 1–2 MeV fast neutrons, and falls back to 5–10 at higher energies. This tool uses the peak value of 20 as a conservative estimate for fast neutrons, which is standard practice when neutron energy is unknown.

Does this tool account for tissue weighting factors?

No. This tool computes equivalent dose (H_T), which uses radiation weighting only. Effective dose (E) further multiplies each organ's equivalent dose by a tissue weighting factor (w_T) and sums across all organs — that requires knowing the irradiated organ and is outside the scope of a simple rad-to-Sv conversion.

Rad to Sieverts Converter

Enter an absorbed dose in rad, select the radiation type, and get the equivalent dose in sieverts using the correct ICRP weighting factor.

Absorbed Dose Input

Dose Value

Input Unit

Radiation Type

ICRP 103 Weighting Factors

Radiation Type	w_R
X-rays, gamma, beta	1
Protons	2
Thermal neutrons	~5
Fast neutrons (peak)	20
Alpha particles	20

Equivalent Dose Result

Sieverts (Sv)

—

Millisieverts (mSv)

—

Microsieverts (µSv)

—

rem (traditional US)

—

Formula

Sv = rad × 0.01 × w_R

0.01 converts rad to gray; w_R is the ICRP radiation weighting factor.

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Summary

The rad (radiation absorbed dose) is the traditional CGS unit for absorbed dose — the energy deposited in tissue per unit mass (1 rad = 0.01 J/kg). The sievert (Sv) expresses equivalent dose, which weights the absorbed dose by a radiation weighting factor (w_R) that reflects the relative biological effectiveness of each radiation type. For X-rays, gamma rays, and beta particles w_R = 1, so 1 rad = 0.01 Sv. For alpha particles w_R = 20, so 1 rad = 0.20 Sv. This tool applies the correct ICRP 103 weighting factors so you get an accurate equivalent dose for any common radiation type.

How it works

Enter the absorbed dose value in the input field.
Select the input unit: rad, millirad (mrad), or microrad (µrad).
Choose the radiation type from the dropdown — the weighting factor (w_R) is shown next to each option.
The tool multiplies the absorbed dose in rad by 0.01 (to convert to gray) and then by w_R to produce equivalent dose in sieverts.
Results are displayed in sieverts (Sv), millisieverts (mSv), and microsieverts (µSv).
Use the Copy buttons to copy any result to the clipboard.

Use cases

Convert legacy rad dose records to sieverts for modern radiation safety reports.
Calculate equivalent dose from alpha, beta, or gamma exposure in health physics coursework.
Verify hand calculations when comparing US (rad/rem) and SI (gray/sievert) literature.
Estimate biological risk weighting when mixing radiation types in a mixed-field environment.
Translate occupational dose limits from rem to sieverts using the correct w_R per source.
Cross-check dosimetry spreadsheets before submitting regulatory filings.

Frequently Asked Questions

Last updated: 2026-07-14 · Reviewed by Nham Vu