Radiation Dose Converter

Radiation measurement is not one quantity with many names. It is four separate physical quantities, each with its own SI unit and its own legacy CGS unit that is still in everyday use across large parts of the world. Absorbed dose answers "how much energy was deposited per kilogram of material?" and is measured in grays or rads. Equivalent dose answers "how much energy was deposited, weighted for the kind of radiation that deposited it?" and is measured in sieverts or rems. Activity answers "how many nuclear transformations happen per second in this source?" and is measured in becquerels or curies. Exposure answers "how much ionisation did X- or gamma radiation produce in air?" and is measured in coulombs per kilogram or roentgens.

This converter gives each quantity its own panel and keeps those panels strictly independent, because no fixed factor connects them. That separation is the whole design point. It is an educational unit-conversion tool: it performs arithmetic on the numbers you type and does nothing more. It does not assess dose, interpret a measurement, or judge whether any number is significant in any context. Dose assessment, monitoring programmes, and the interpretation of any radiation measurement belong to qualified radiation-protection professionals working under the applicable regulatory framework.

How to Use the Radiation Dose Converter

1. Identify which quantity you actually have. A dosimeter badge report is almost always an equivalent or effective dose (mSv, mrem). A radiotherapy or radiobiology figure describing energy deposition is an absorbed dose (Gy, rad). A number describing a source, sample, or contamination measurement is an activity (Bq, Ci). A reading from an older survey instrument calibrated in R/h is an exposure rate. Choosing the wrong panel is the one mistake this tool cannot catch for you.
2. Type your value into any field on the matching panel. Every other field on that same panel recomputes immediately through the panel's SI pivot unit, gray, sievert, becquerel, or coulomb per kilogram.
3. Read the reference row at the bottom. It shows the current SI value on all four panels side by side, so you can see at a glance what state each panel is in.
4. Do not move numbers between panels. The converter deliberately refuses to link them, and so should you. Converting gray to sievert requires a radiation weighting factor; converting activity to dose requires geometry, source energy, shielding, and a dose coefficient. Neither is arithmetic.
5. Scientific notation works. Type 3.7e10 into the becquerel field or 2.58e-4 into the coulomb-per-kilogram field; the parser handles exponent notation directly. Invalid or partial input (an empty field, a lone minus sign, stray letters) simply leaves the other fields untouched rather than filling them with nonsense.

The Quantities and Their Units

Absorbed dose (D), SI unit the gray (Gy). One gray is one joule of energy imparted by ionising radiation per kilogram of matter: 1 Gy = 1 J/kg. It is a purely physical quantity, it describes energy deposition and says nothing about what kind of radiation deposited it or what tissue received it. The legacy unit is the rad (radiation absorbed dose), defined as 100 ergs per gram, which works out to exactly 0.01 Gy. So 1 Gy = 100 rad exactly, and 1 rad = 10 mGy. The millirad follows: 1 mrad = 10 µGy = 1e-5 Gy.

Equivalent dose (H), SI unit the sievert (Sv). Equivalent dose is absorbed dose multiplied by a radiation weighting factor: H = Σ w_R · D_R, summed over each type of radiation R present. The weighting factor is dimensionless, so the sievert also carries SI dimensions of J/kg, the same dimensions as the gray. That shared dimension is precisely why the two units get confused, and why the SI system gives them separate names in the first place. The legacy unit is the rem (roentgen equivalent man), exactly 0.01 Sv, so 1 Sv = 100 rem exactly. Because the SI prefixes are decimal, 1 Sv = 1000 mSv = 1 000 000 µSv, and the cross-system relation 1 mSv = 100 mrem follows directly.

Activity (A), SI unit the becquerel (Bq). One becquerel is one nuclear transformation per second: 1 Bq = 1 s⁻¹. It describes the source, not the radiation field around it and certainly not the dose to anything. The legacy unit is the curie, historically tied to the activity of radium but now defined as exactly 1 Ci = 3.7 × 10¹⁰ Bq. Because the becquerel is such a small unit, laboratory and medical work uses kBq, MBq, and GBq freely; the curie side uses mCi and µCi. Two useful shortcuts: 1 mCi = 37 MBq and 1 µCi = 37 kBq, both exact.

Exposure (X), SI unit the coulomb per kilogram (C/kg). Exposure measures the electric charge liberated by X- or gamma radiation per unit mass of air. It is defined only for air and only for photons, which makes it the narrowest of the four quantities. The legacy unit is the roentgen, defined as exactly 1 R = 2.58 × 10⁻⁴ C/kg. The milliroentgen follows: 1 mR = 2.58 × 10⁻⁷ C/kg. Modern instruments increasingly report air kerma or ambient dose equivalent instead, but roentgen-calibrated survey meters remain in service and their readings still need converting.

All four conversion factors used by this tool are exact by definition. None of them is a rounded empirical value, so round-trip conversions are limited only by floating-point representation, not by the factor itself.

Worked Examples

Example 1, Gray to rad. Convert 1 Gy to rad. Divide by the factor 0.01 Gy per rad: 1 ÷ 0.01 = 100 rad. Reversing, 100 rad × 0.01 = 1 Gy. In the smaller prefixes, 1 Gy = 1000 mGy = 1 000 000 µGy = 100 000 mrad.

Example 2, Millisievert to millirem. Convert 1 mSv to mrem. First pivot to sieverts: 1 mSv = 1e-3 Sv. Then divide by the millirem factor 1e-5 Sv per mrem: 1e-3 ÷ 1e-5 = 100 mrem. The general rule is that the mSv-to-mrem factor is the same 100 as the Sv-to-rem factor, because both prefixes are milli.

Example 3, Curie to becquerel. Convert 1 Ci to Bq. Multiply by the exact definition: 1 × 3.7e10 = 3.7 × 10¹⁰ Bq = 37 GBq. Working downward, 1 mCi = 3.7 × 10⁷ Bq = 37 MBq, and 1 µCi = 3.7 × 10⁴ Bq = 37 kBq.

Example 4, Roentgen to coulomb per kilogram. Convert 1 R to C/kg. Multiply by the exact definition: 1 × 2.58e-4 = 2.58 × 10⁻⁴ C/kg = 0.258 mC/kg = 258 µC/kg. A reading of 1 mR is therefore 2.58 × 10⁻⁷ C/kg.

Example 5, Microsievert to millirem. Convert 5 µSv to mrem. Pivot to sieverts: 5 µSv = 5e-6 Sv. Divide by 1e-5 Sv per mrem: 5e-6 ÷ 1e-5 = 0.5 mrem. The handy rule that falls out of this is 1 µSv = 0.1 mrem, or equivalently 10 µSv = 1 mrem.

Example 6, Megabecquerel to microcurie. Convert 3.7 MBq to µCi. Pivot to becquerels: 3.7 MBq = 3.7 × 10⁶ Bq. Divide by 3.7 × 10⁴ Bq per µCi: 3.7e6 ÷ 3.7e4 = 100 µCi. The 3.7 cancels cleanly, which is why activity conversions with a leading 3.7 are so common in worked problems.

Where Radiation Unit Conversion Shows Up

Cross-border and cross-generation documents. SI units (Gy, Sv, Bq) are the international standard, but the older CGS units (rad, rem, Ci, R) remain in wide use in the United States and appear throughout older literature, equipment labels, and archived records everywhere. Reading a 1970s technical report alongside a modern one means converting constantly.

Instrumentation. Survey meters, dosimeters, and contamination monitors are calibrated in whatever unit family their market expects. A single facility can easily hold instruments reading in µSv/h, mR/h, and cpm-converted-to-Bq, and reconciling their outputs is routine unit arithmetic.

Nuclear medicine and radiopharmacy. Administered activities are quoted in MBq in most of the world and in mCi in the United States. The 1 mCi = 37 MBq identity is one of the most-used conversions in the field.

Radiotherapy and radiobiology. Treatment planning and cell-survival work are expressed in absorbed dose (Gy), because what matters there is energy deposited in a defined volume. Older literature uses rads for the same quantity, so a factor of 100 sits between a 1975 paper and a 2025 one.

Environmental monitoring and nuclear-industry reporting. Environmental sample activities span an enormous range, from Bq/kg in soil surveys to TBq in facility inventories, and reports frequently mix SI prefixes with legacy curie figures inherited from older datasets.

Teaching and exam work. Physics and health-physics courses routinely test whether a student knows that the gray and sievert are not interchangeable. Getting the unit family right is usually worth more marks than the arithmetic itself.

Common Mistakes

Treating gray and sievert as the same unit. This is by far the most common error, and it is an easy one to make: both have SI dimensions of J/kg, both are named after a physicist, and both show up in the same documents. But the gray measures energy deposited, full stop, while the sievert measures that energy after weighting for the type of radiation that delivered it. There is no fixed number that converts Gy to Sv. The step requires a radiation weighting factor drawn from the applicable standard, which depends on the radiation type and, for effective dose, on the tissues involved. This converter keeps the two panels separate specifically so it cannot be used to fake that step. The same applies in reverse: a sievert figure cannot be turned back into a gray figure without knowing the weighting that was applied.

Trying to convert activity into dose. Becquerels describe a source; sieverts and grays describe what happens to matter. Getting from one to the other requires the source's emitted energies and branching ratios, the geometry and distance, any shielding, the exposure duration, and, for internal exposure, a biokinetic model and dose coefficient. No unit factor exists, and any tool that offers one without those inputs is guessing.

Mixing prefix and unit-family conversions in one step. Going from µSv to mrem involves two factors: the SI prefix step and the Sv-to-rem step. Doing them in one mental jump is where the stray factors of 10 come from. Pivot to the SI base unit first, then convert unit family, then apply the target prefix. That is exactly the order the converter uses internally.

Assuming exposure equals absorbed dose. Exposure (R, C/kg) is defined only for photons interacting in air. It is not absorbed dose in tissue, and treating a roentgen figure as though it were a rad or gray figure conflates two different definitions with two different reference materials.

Confusing equivalent dose with effective dose. Both are reported in sieverts. Equivalent dose applies a radiation weighting factor to a specific organ or tissue; effective dose additionally applies tissue weighting factors and sums over the body. Same unit, different quantities, always check which one a document means.

Dropping the "per hour" when converting rates. Dose-rate conversions use the identical factors as dose conversions, because the time unit cancels. But a number carried across without its time unit becomes meaningless, and mixing an hourly rate with a cumulative dose is a classic reporting error.

Frequently Asked Questions

Why do the gray and the sievert both equal one joule per kilogram if they are different units?

Because the radiation weighting factor that turns absorbed dose into equivalent dose is dimensionless. Multiplying J/kg by a pure number leaves J/kg. The SI system gives the two quantities distinct unit names precisely so that a document can make clear which quantity it means, since the dimensions alone cannot distinguish them. The names carry the information that the dimensions do not.

Can I convert grays to sieverts with this tool?

No, and that is deliberate. Converting absorbed dose to equivalent dose requires a radiation weighting factor that depends on the type of radiation involved, taken from the applicable standard. That is a physics-and-standards question, not a unit conversion, and it is not something a general-purpose converter should be doing on your behalf. The four panels in this tool are independent for exactly this reason.

What is the difference between the rad and the rem?

The rad is the legacy unit of absorbed dose (1 rad = 0.01 Gy). The rem is the legacy unit of equivalent dose (1 rem = 0.01 Sv). They stand in exactly the same relationship to each other as the gray and the sievert do, same numerical factor to their SI counterparts, but different quantities. A number in rads cannot be relabelled as rems any more than a number in grays can be relabelled as sieverts.

Is 1 Ci = 3.7 × 10¹⁰ Bq an approximation?

No, it is exact by definition. The curie was originally tied to the activity of one gram of radium-226, but it was later fixed at exactly 3.7 × 10¹⁰ conversions per second so that it would be a stable, well-defined unit independent of any measurement of radium. The same applies to the roentgen at exactly 2.58 × 10⁻⁴ C/kg.

Does the converter work for dose rates as well as doses?

Yes, for the arithmetic. Because the time unit appears identically on both sides of the conversion, Gy/h to rad/h uses the same factor of 100 as Gy to rad, and µSv/h to mrem/h uses the same factor as µSv to mrem. Convert the numerical part and carry the time unit through unchanged. Just be careful never to compare a rate against a cumulative total without accounting for the duration.

Why does exposure still exist as a quantity if we have absorbed dose?

Historically, exposure came first, ionisation in air was what early instruments could actually measure, long before absorbed dose in tissue could be quantified. A great deal of legacy data, and a great many still-serviceable instruments, are expressed in roentgens. Modern practice generally prefers air kerma or ambient dose equivalent, but the roentgen has not disappeared from the field, so the conversion is still needed.

What is the relationship between equivalent dose and effective dose, given both use the sievert?

Equivalent dose weights absorbed dose for the type of radiation and applies to a specified organ or tissue. Effective dose takes those organ equivalent doses, weights each by a tissue weighting factor, and sums them to give a single whole-body figure. Both are reported in sieverts, so the unit alone will not tell you which one a document means, the surrounding text has to.

can the Radiation Dose Converter (Gy, rad, Sv, rem, Bq, Ci, C/kg, R) be used for professional or commercial purposes?

It provides mathematically correct unit conversions using exact, standards-defined factors, so the arithmetic is sound for professional and educational use. It is a converter only: it does not assess dose, evaluate exposure, or produce any output that could substitute for a radiation-protection assessment. Any decision arising from a radiation measurement should be made by a qualified radiation-protection professional under the applicable regulatory framework.

How often are the underlying conversion factors updated?

Essentially never, because all four are exact by definition rather than measured. The gray-to-rad, sievert-to-rem, curie-to-becquerel, and roentgen-to-coulomb-per-kilogram factors have been fixed for decades. What does change over time is the guidance surrounding weighting factors and the quantities recommended for practical measurement, and those live in the standards documents listed below, not in the unit conversions themselves.

References

• BIPM, The International System of Units (SI Brochure, 9th edition). For the Radiation Dose Converter (Gy, rad, Sv, rem, Bq, Ci, C/kg, R), Published by the Bureau International des Poids et Mesures. The canonical definition of the SI, including the derived units with special names for ionising radiation: the becquerel (activity), the gray (absorbed dose), and the sievert (equivalent dose), together with the explanation of why the gray and sievert have distinct names despite sharing the dimension J/kg.
• ICRU Report 85, Fundamental Quantities and Units for Ionizing Radiation. Published by the International Commission on Radiation Units and Measurements. The authoritative definitions of absorbed dose, kerma, exposure, equivalent dose, and the operational quantities, along with the distinctions between them.
• ISO 80000-10, Quantities and units, Part 10: Atomic and nuclear physics. The international standard specifying the names, symbols, and definitions of atomic and nuclear quantities, including activity, absorbed dose, equivalent dose, and exposure, and their SI units.
• NIST Special Publication 811, Guide for the Use of the International System of Units (SI). The US reference for SI usage and unit conversion, whose appendix tables give the exact conversion factors for the legacy units used here: 1 rad = 0.01 Gy, 1 rem = 0.01 Sv, 1 Ci = 3.7 × 10¹⁰ Bq, and 1 R = 2.58 × 10⁻⁴ C/kg.
• ICRP publications on radiological protection quantities. The International Commission on Radiological Protection is the body that defines and periodically reviews the radiation weighting factors and tissue weighting factors used to derive equivalent dose and effective dose from absorbed dose. Those factors are the reason gray-to-sievert is not a unit conversion, and any such calculation should reference the ICRP publication in force for the applicable regulatory framework.