What is being measured?
Radiation exposure follows the stated ionization-in-air convention and is kept separate from dose and activity. No clinical effect or exposure limit is inferred.
Exposure for X/gamma radiation; not absorbed dose. Do not convert roentgens to grays as a unit conversion.
Meaning of R
Roentgens uses the symbol R in this library and measures photon radiation exposure. Under the stated reference convention, 1 R = approximately 0.000258 C/kg. This equivalence changes how a known value is written. It does not increase measurement accuracy or establish whether a measurement is appropriate to a real application.
Conversion method
Multiply the value by the source factor (0.000258), then divide by the target factor (1). The factor ratio expresses the same photon radiation exposure measurement in the other unit.
Worked example
For a known value of 10 R, the reference conversion gives 0.00258 C/kg. Converting that result back gives approximately 10 R. This reverse check helps catch a reversed factor, but matching round-trip arithmetic alone does not independently verify a source definition.
Common reference values
| Input (R) | Reference equivalent (C/kg) |
|---|---|
| 1 | 0.000258 |
| 5 | 0.00129 |
| 10 | 0.00258 |
| 25 | 0.00645 |
| 50 | 0.0129 |
| 100 | 0.0258 |
Compare one R with other units
| Target unit | Equivalent of 1 R | Definition guide |
|---|---|---|
| Coulombs per kilogram (C/kg) | 0.000258 | Read definition |
| Millicoulombs per kilogram (mC/kg) | 0.258 | Read definition |
| Microcoulombs per kilogram (µC/kg) | 258 | Read definition |
| Milliroentgens (mR) | 1000 | Read definition |
Precision and common mistakes
- Keep the source and target quantity consistent. A matching symbol is not enough to establish a compatible definition.
- Record the original measurement precision. Showing twelve significant digits in a table does not make a rounded input more precise.
- Check symbol capitalization, prefixes and any regional convention in the source. Use the displayed unit definition rather than a similarly named unit.
- Factors involving repeating fractions or π use finite numerical precision. Round the final answer to the precision justified by your input.
Unit reference only. These pages do not assess biological effects, clinical use, exposure limits or radiation safety. Absorbed dose, equivalent dose, activity and exposure remain different quantities; unit scaling cannot convert one into another.
Use a working converter
- Photon radiation exposure converter
- Roentgens to Coulombs per kilogram converter
- Roentgens to Millicoulombs per kilogram converter
- Roentgens to Microcoulombs per kilogram converter
- Roentgens to Milliroentgens converter
Source and verification scope
Examples and tables are computed from the versioned unit definitions used by the linked converters. The source access dates appear below. Computandum is independent of the cited organizations; a citation does not mean that a publisher endorses this page or an actual project.