Convert radiation exposure in air between C/kg, mC/kg, µC/kg, roentgen, and milliroentgen, then compare SI and legacy exposure scales on one sheet.
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Radiology Reference
A radiation exposure converter is useful when older roentgen-based references need to be compared with SI coulomb-per-kilogram notation. This page keeps the quantity boundary explicit: exposure is an ionization-in-air quantity for photons such as X-rays and gamma rays, not a source-activity or absorbed-dose result.
Exposure measures the amount of ionization produced in air by X-rays or gamma rays. In the coherent SI system, that quantity is expressed in coulombs per kilogram of air.
That makes exposure different from source activity and different from absorbed or effective dose. The units may all appear in radiation discussions, but they do not answer the same question.
Roentgen remains common in older radiology, radiation-survey, and educational material even though SI reporting prefers coulomb per kilogram. A converter helps bridge those systems without losing the exact scale relationship.
This is especially useful when historical records, U.S. references, or survey-instrument documentation mix roentgen and SI exposure notation on the same topic.
1 R = 2.58 × 10^-4 C/kg of air
Standard relationship between roentgen and the SI exposure unit.
1 mR = 2.58 × 10^-7 C/kg
Scaled legacy-to-SI relationship for milliroentgen readings.
Exposure is useful for air-ionization reference work, but it does not replace dose or activity calculations. If the real question is what a person absorbed, what a source emits, or what dose equivalent should be reported, you need a different quantity and usually more context.
This page therefore stays on the exposure scale only and does not imply medical, biological, or regulatory interpretation from the unit conversion alone.
Frequently asked questions
1 roentgen equals 0.000258 coulomb per kilogram of air, or 2.58 × 10^-4 C/kg.
No. Exposure is an air-ionization quantity for photons, while dose describes energy deposited in material or biological effect under a particular framework.
Because the exposure quantity and the roentgen definition are tied to ionization in air rather than to absorbed energy in tissue or another material.
Use a dose converter when the source is already reporting gray, rad, sievert, or rem, or when the question is about absorbed or effective dose rather than exposure in air.
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