How to use the converter
Pick the unit you have and the unit you want. Conversion between units of the same quantity uses exact factors. Gray–sievert weighting requires the stated tissue-dose quantity and a named radiation type and weighting set. Exposure converts exactly between R and C/kg; its conversion to air kerma is approximate.
Press Simulate to load a reviewed conversion example. Each example is labelled published or hypothetical.
Quantities and units
Absorbed dose is energy imparted by ionizing radiation per unit mass of material, expressed in gray or rad. Dose equivalent applies a quality factor to absorbed dose at a point in tissue. Equivalent dose applies radiation weighting factors to mean absorbed doses in an organ or tissue. Exposure describes charge liberated by x-rays or gamma rays in air, expressed in C/kg or roentgen. Air kerma describes energy transferred from a photon beam to air per unit mass and is expressed in gray.
Gray to sievert
The NRC options use the quality factors in 10 CFR 20.1004 Table 1004(b).1. The ICRP 103 set shown here uses the fixed radiation weighting factors printed in Canada Radiation Protection Regulations Schedule 2.
| Radiation and set | Factor |
|---|---|
| X-, gamma, or beta radiation (NRC) | Q = 1 |
| Alpha particles, multiple-charged particles, fission fragments and heavy particles of unknown charge (NRC) | Q = 20 |
| Neutrons of unknown energy (NRC) | Q = 10 |
| High-energy protons (NRC) | Q = 10 |
| Photons, all energies (ICRP 103 set via Canada) | wR = 1 |
| Electrons and muons, all energies, excluding Auger electrons emitted from nuclei bound to DNA (ICRP 103 set via Canada) | wR = 1 |
| Protons and charged pions (ICRP 103 set via Canada) | wR = 2 |
| Alpha particles, fission fragments and heavy ions (ICRP 103 set via Canada) | wR = 20 |
For one radiation type, multiply absorbed dose in tissue by Q to obtain NRC dose equivalent, or mean absorbed dose in an organ or tissue by wR to obtain equivalent dose. Reverse conversion divides the corresponding single-radiation-type quantity by the same factor.
High-energy protons have Q = 10 in the NRC table; protons have wR = 2 in Canada Schedule 2. Selecting the set therefore changes this example fivefold.
Known-energy neutron calculations require energy information and are outside this converter; see 10 CFR 20.1004(c). In the ICRP 103 set, the neutron weighting factor is a continuous function of neutron energy (Canada Schedule 2, item 5); this converter does not offer it.
Roentgen and air kerma
The exposure definition gives 1 R = 2.58 × 10⁻⁴ C/kg exactly. NIST relates exposure to air kerma using Kair = X × (W/e)/(1 − g), where X is in C/kg, W/e = 33.97 J/C, and g is the fraction of secondary-electron energy lost through radiative processes.
This converter neglects radiative losses, giving Kair ≈ X × 33.97 J/C and approximately 8.764 mGy per R. The exposure-conversion path estimates air kerma, not absorbed dose in tissue or bone.
NIST gives g = 0.0016 for Cs-137 and 0.0032 for Co-60; including those values gives approximately 8.778 and 8.792 mGy per R, respectively.
Why a CT dose index is not effective dose
The weighting calculation requires absorbed dose in tissue for the selected radiation type. A CT dose index or air kerma does not by itself supply that input. Do not enter CTDIvol or air kerma into the gray–sievert weighting path.
Effective dose combines equivalent doses across organs and tissues using tissue weighting factors. This converter does not derive effective dose from an absorbed dose, CTDIvol, DLP or DAP.
SI and legacy units
Gray, sievert and coulomb per kilogram are SI units. The cited US regulations also use the legacy units rad, rem and roentgen.
Rates
The same factors convert rates when both values use the same time unit, for example 1 µSv/h = 0.1 mrem/h. This calculator does not change the time unit.
Display precision
Unit and weighting results are displayed to at most six significant figures; exposure–air-kerma approximations use four. Calculations retain the unrounded value. The ≈ symbol marks display rounding or the air-kerma approximation; it is not a measurement-uncertainty estimate.
Source versions
The NRC published a proposal in July 2026 to allow alternative dosimetry methods, including tissue and radiation weighting factors. The eCFR text current to 3 November 2026 retains 10 CFR 20.1004(a)–(c).
Worked example
10 CFR 20.1004 gives alpha particles a quality factor of 20, so 0.05 Gy of absorbed dose is 1 Sv of dose equivalent (Table 1004(b).1).
| Item | Value |
|---|---|
| Value | 0.05 |
| From | Gy (gray) |
| To | Sv (sievert) |
| Radiation type | Alpha particles, multiple-charged particles, fission fragments and heavy particles of unknown charge (NRC Q = 20) |
| Dose equivalent | 1 Sv |
Dose equivalent for the selected radiation type, not effective dose.
Frequently asked questions
How many mrem is 1 mSv?
100 mrem. 1 rem = 0.01 Sv (10 CFR 20.1004), so 1 mSv = 0.1 rem = 100 mrem.
How many mSv is 1 rem?
10 mSv (1 rem = 0.01 Sv).
Is 1 rad equal to 1 rem?
They measure different quantities. Under the NRC quality-factor calculation, 1 rad of absorbed dose in tissue gives 1 rem of dose equivalent when Q = 1; see Gray to sievert.
Can you convert roentgen to rem or sievert?
This converter does not convert exposure to rem or sievert. Exposure in air alone does not supply the absorbed dose in tissue needed for that calculation.
How do you convert Gy to Sv?
For one named radiation type, multiply absorbed dose in tissue in Gy by its NRC quality factor to obtain dose equivalent in Sv, or mean absorbed dose in an organ or tissue in Gy by its ICRP 103 radiation weighting factor to obtain equivalent dose in Sv. This converter implements the ICRP 103 set from Canada Schedule 2; see Gray to sievert.
Is mGy the same as mSv?
No. mGy and mSv label different quantities; see Why a CT dose index is not effective dose.
How many microsieverts are in a millisievert?
1,000 (milli = 10⁻³, micro = 10⁻⁶; BIPM SI Brochure Table 7).
References
- US Nuclear Regulatory Commission. 10 CFR Part 20, Standards for Protection Against Radiation: § 20.1003 Definitions and § 20.1004 Units of radiation dose. eCFR, title 10 current to 3 November 2026. https://www.ecfr.gov/current/title-10/chapter-I/part-20/subpart-A/section-20.1004
- Thompson A, Taylor BN. Guide for the Use of the International System of Units (SI). NIST Special Publication 811, 2008 edition. Gaithersburg, MD: NIST; 2008. https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication811e2008.pdf
- Bureau International des Poids et Mesures. The International System of Units (SI). 9th edition 2019, version 4.01, June 2026. https://www.bipm.org/documents/20126/41483022/SI-Brochure-9-EN.pdf
- NIST Radiation Physics Division. RPD-P-05, Irradiation of Passive Dosimeters. Version 7.00, 29 May 2025. https://www.nist.gov/document/rpd-procedure-5-version-7
- ICRP. The 2007 Recommendations of the International Commission on Radiological Protection. ICRP Publication 103. Ann ICRP 2007;37(2-4). Executive summary and glossary (free extract). https://www.icrp.org/publication.asp?id=ICRP%20Publication%20103
- Canada. Radiation Protection Regulations, SOR/2000-203, Schedule 2, Radiation Weighting Factors. Consolidation current to 19 October 2026. https://laws-lois.justice.gc.ca/eng/regulations/SOR-2000-203/
- Butcher KS, Crown LD, Gentry EJ. The International System of Units (SI): Conversion Factors for General Use. NIST Special Publication 1038. Gaithersburg, MD: NIST; 2006. https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication1038.pdf
- US Nuclear Regulatory Commission. Reforming and Modernizing the NRC’s Radiation Protection Framework; Proposed Rule. Fed Regist 2026;91(134):43456-43504 (15 July 2026). Docket NRC-2025-1140. https://www.govinfo.gov/content/pkg/FR-2026-07-15/html/2026-14208.htm
- US HHS/ASPR. Radiation Emergency Medical Management (REMM). Radiation Units and Conversion Factors. https://remm.hhs.gov/radmeasurement.htm
- US Food and Drug Administration. 21 CFR 1020.30, Diagnostic x-ray systems and their major components, §1020.30(k). https://www.ecfr.gov/current/title-21/chapter-I/subchapter-J/part-1020/section-1020.30
- US Food and Drug Administration. 21 CFR 1020.32, Fluoroscopic equipment, §1020.32(d)(2)(ii). https://www.ecfr.gov/current/title-21/chapter-I/subchapter-J/part-1020/section-1020.32