Radiation Dose Converter
Same value in every unit
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Absorbed dose and equivalent dose are not the same quantity
The most common error with radiation units is treating gray and sievert as interchangeable. The gray is absorbed dose: one joule of energy deposited per kilogram of matter. The sievert is equivalent dose: that same absorbed dose multiplied by a radiation weighting factor accounting for how much biological damage that radiation type does per joule deposited.
For X-rays, gamma rays and beta particles the weighting factor is 1, so 1 mGy and 1 mSv come out numerically identical and people conclude the units are the same thing. They are not. For alpha particles the ICRP 103 weighting factor is 20, so 1 Gy absorbed corresponds to 20 Sv equivalent. Going from gray to sievert is a calculation that requires knowing what the radiation was. It is not a unit conversion, and no converter can do it from a bare number.
What this converter does
It converts within each family. On the absorbed side: gray, milligray, microgray and rad. On the equivalent side: sievert, millisievert, microsievert, rem and millirem. Both families scale identically between the SI and the older units, which is exactly why the two columns look deceptively similar. The sievert also carries effective dose, which sums tissue-weighted organ doses across the whole body: same unit, different quantity again.
Reference points
- 1 Gy = 1 joule per kilogram
- 1 Gy = 100 rad; 1 rad = 0.01 Gy (exact)
- 1 Sv = 100 rem; 1 rem = 0.01 Sv (exact)
- 1 mSv = 100 mrem; 1 µSv = 0.1 mrem
- Radiation weighting factors, ICRP 103: 1 for photons and electrons, 2 for protons, 20 for alpha particles, fission fragments and heavy ions; for neutrons the factor varies continuously with energy
- Those weighting factors are a radiological protection convention, not measured constants. Earlier recommendations and some national regulations use different values, so use the set your regulator applies
rad and rem are the older non-SI units, still in routine use in the United States. Gy and Sv are the SI units used elsewhere.
Not medical or safety advice
This page converts numbers. It says nothing about whether any dose is acceptable, and quotes no limits or thresholds by design. If you are interpreting a scan report, a dosimeter reading, an occupational dose record or a suspected exposure, take it to a medical physicist, a radiation protection adviser or your national regulator. Checking arithmetic is not a dose assessment.
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Frequently Asked Questions
They are numerically equal only when the radiation weighting factor is 1, which covers X-rays, gamma rays and beta particles (electrons). Gray measures absorbed dose, the joules deposited per kilogram; sievert measures that absorbed dose after weighting for how damaging the radiation type is. For alpha particles the ICRP 103 weighting factor is 20, so 1 Gy absorbed corresponds to 20 Sv equivalent. Both quantities are dimensionally joules per kilogram, which is why the confusion is so persistent.
Not as a unit conversion, because you need to know the radiation type first. Equivalent dose in sieverts equals absorbed dose in grays multiplied by the radiation weighting factor: under ICRP 103 that is 1 for photons and electrons, 2 for protons, 20 for alpha particles, fission fragments and heavy ions, and an energy-dependent value for neutrons. Older schemes differ, ICRP 60 put protons at 5, and some national rules still use quality factors instead. This converter therefore works inside each family only: Gy to rad, Sv to rem.
100 millirem. The relationship is exact by definition: 1 Sv = 100 rem, so 1 mSv = 100 mrem and 1 microsievert = 0.1 mrem. The same factor applies on the absorbed side, where 1 Gy = 100 rad. The rem and rad are the older non-SI units, still in routine regulatory use in the United States, while the sievert and gray are the SI units used elsewhere.
The same distinction as gray versus sievert, expressed in the older CGS-era units: rad is absorbed dose, rem is equivalent dose. 1 rad = 0.01 Gy and 1 rem = 0.01 Sv, both exact. Converting rad to rem needs the radiation weighting factor exactly as gray to sievert does, so it is not a straight numerical swap. The two coincide for X-rays, gamma rays and beta particles, and diverge sharply for alpha particles.
They report different quantities. Imaging equipment reports absorbed dose and machine dose indices in mGy: a CT CTDIvol, for example, is measured in a standard plastic phantom rather than in your body. Personal dosimeters report an operational quantity, personal dose equivalent such as Hp(10), in mSv, because dose records and regulations are written in sieverts. The two figures are not interchangeable. Take any question about a real exposure to a medical physicist or radiation protection adviser.
No, because neither is a dose unit in this sense. The roentgen measures exposure, the ionisation produced in air, defined as 2.58 x 10^-4 coulomb per kilogram; turning that into absorbed dose in tissue depends on the medium and the photon energy, so there is no single fixed factor. The becquerel measures activity, one nuclear decay per second in a source, which tells you nothing about dose without geometry, distance, shielding and exposure time.