Radiation Exposure Converter
ScienceConvert radiation exposure between roentgen, milliroentgen, and coulombs per kilogram — distinct from radiation dose and radioactivity units.
From
To
All conversionsfor 1 Roentgen (R)
| Coulombs per Kilogram (C/kg) | 0.000258 |
| Roentgen (R) | 1 |
| Milliroentgen (mR) | 1000 |
What is a Radiation Exposure?
The Radiation Exposure Converter converts radiation exposure between coulombs per kilogram (the SI unit) and roentgen/milliroentgen (the legacy units). Radiation exposure specifically measures how much ionisation X-rays or gamma rays produce in a given mass of air — a distinct quantity from radiation dose (energy absorbed by tissue, covered by the Radiation Dose Converter) and radioactivity (decay rate, covered by the Radioactivity Converter).
Enter a value in any supported unit and the converter calculates the equivalent instantly.
How to use this Radiation Exposure calculator
- Choose your starting unit from the source dropdown — for example, "Roentgen (R)".
- Enter the numeric value you want to convert in the input field.
- Choose your target unit from the destination dropdown — for example, "Coulombs per Kilogram (C/kg)".
- Read the converted result, which updates instantly as you type or change units.
- Use the swap (⇅) button if you need to reverse the conversion direction.
- Use the copy button to grab the result for a historical record review or equipment documentation comparison.
Formula & Methodology
The converter's base unit is coulombs per kilogram (C/kg). Every supported unit has a fixed multiplier: - 1 roentgen (R) = 0.000258 C/kg (exactly 2.58 × 10⁻⁴ C/kg, by definition) - 1 milliroentgen (mR) = 0.000000258 C/kg Any conversion follows: Result = Input × (toBase of source unit ÷ toBase of target unit) Worked example — converting 100 milliroentgen to coulombs per kilogram: Result = 100 × 0.000000258 = 0.0000258 C/kg This confirms how a legacy exposure reading from older X-ray equipment translates to the modern SI unit.
Frequently Asked Questions
Radiation exposure specifically measures the amount of ionisation X-rays or gamma rays produce in a given mass of air, expressed in roentgen or coulombs per kilogram, while [radiation dose](/radiation-dose-converter/) (sievert, gray) measures the energy absorbed by tissue or material. Exposure is an older, more specific measurement historically tied to air ionisation chambers, while dose is the more general modern quantity.
Multiply the roentgen value by 0.000258, since one roentgen equals exactly 2.58 × 10⁻⁴ coulombs per kilogram by definition. Enter your value with 'Roentgen (R)' as the source and 'Coulombs per Kilogram (C/kg)' as the target to apply this automatically.
The roentgen predates the SI system and was specifically defined around X-ray ionisation measurement in air using early ionisation chamber technology — modern radiation protection has largely moved to dose-based units (sievert, gray) that better represent biological effect, though roentgen still appears in some older equipment and documentation, particularly in medical and industrial X-ray contexts.
A typical diagnostic X-ray might produce an exposure in the range of a few milliroentgen at the point of measurement, though this varies significantly based on the specific procedure, equipment, and body part being imaged.
The roentgen and C/kg exposure units were specifically defined based on ionisation of air by X-rays and gamma rays, so they don't directly apply to other radiation types like alpha or beta particles, which is one reason the more general dose-based units (sievert, gray) became the modern standard covering all radiation types.
For X-rays and gamma rays in soft tissue, 1 roentgen of exposure corresponds to approximately 0.01 gray (1 rad) of absorbed dose, though this relationship depends on the specific material being irradiated — exposure measures ionisation in air specifically, while dose measures energy absorbed in the actual material of interest.
Older radiation measurement equipment, particularly ionisation chamber-based instruments used in medical and industrial X-ray facilities, was originally calibrated in roentgen, and some of this legacy equipment remains in service, requiring occasional conversion to modern SI units for reporting or comparison.
Exposure is traditionally measured using an ionisation chamber, which detects the electrical charge produced when X-rays or gamma rays ionise the air within a known volume — this direct measurement of ionisation is exactly what the roentgen and C/kg units quantify.
This converter handles exposure (ionisation in air from X-rays/gamma rays, in roentgen/C/kg), while the [Radioactivity Converter](/radioactivity-converter/) handles decay activity (how many atoms in a radioactive source decay per second, in curie/becquerel) — these measure fundamentally different things: one is about radiation's effect on air, the other is about a source's decay rate.
While dose-based units (sievert, gray) are now the international standard for radiation protection and safety limits, understanding exposure and being able to convert from legacy roentgen-based equipment or documentation remains useful for reviewing historical records and older instrumentation still in use.
Also known as