About the Radiation Unit Converter
Radiation is described by four different quantities, and each has an SI unit and an older traditional unit. This radiation unit converter handles all of them: equivalent and effective dose (sievert and rem), absorbed dose (gray and rad), radioactivity (becquerel, curie and disintegrations per minute) and exposure in air (coulomb per kilogram and roentgen), with the usual milli-, micro- and other prefixes.
It is meant for students, health-physics and lab workers, radon testers, emergency planners and anyone reading a dosimeter, a news report or an older US document that uses rem, rad or curies. Pick the quantity first, then the two units.
The converter only changes units within one quantity. Sieverts cannot be converted to grays, or becquerels to sieverts, without knowing the radiation type, energy, organ and exposure geometry, so those conversions are deliberately not offered. This is a unit conversion tool, not a dose assessment.
How to use the radiation unit converter
- 1Choose the quantity: dose, absorbed dose, activity or exposure.
- 2Enter the number you want to convert.
- 3Pick the unit it is in and the unit you want.
- 4Read the result, the SI and traditional equivalents, and the full table.
Formula and method
The traditional units are defined exactly in terms of the SI units: one rem is 0.01 sievert, one rad is 0.01 gray (0.01 J/kg), one curie is 3.7 × 10¹⁰ becquerels (decays per second, originally the activity of one gram of radium-226) and one roentgen is 2.58 × 10⁻⁴ coulombs of ionisation per kilogram of air. The converter multiplies your value by the size of the source unit in SI and divides by the size of the target unit.
Sieverts and grays both equal joules per kilogram, but the sievert includes weighting factors for radiation type and tissue sensitivity, so the two are only numerically equal for X-rays, gamma and beta radiation. Becquerels and curies measure how fast a source decays, not the dose anyone receives.
- Sv
- Sievert — equivalent or effective dose
- Gy
- Gray — absorbed dose, 1 J/kg
- Bq
- Becquerel — one decay per second
- C/kg
- Coulomb per kilogram — exposure (ionisation in air)
Worked examples
1 rem in millisieverts
One rem is 0.01 Sv, which is 10 mSv. US documents often quote limits in rem while international ones use mSv.
100 mrem in mSv
100 mrem × 0.00001 Sv/mrem = 0.001 Sv = 1 mSv. A handy rule: divide millirem by 100 to get millisieverts.
1 microcurie lab source in becquerels
A curie is 3.7 × 10¹⁰ Bq, so a microcurie is 3.7 × 10⁴ = 37,000 decays per second (37 kBq).
2 gray in rad
One rad is 0.01 Gy, so 2 Gy ÷ 0.01 = 200 rad.
1 roentgen in µC/kg
One roentgen is defined as 2.58 × 10⁻⁴ C/kg, which is 258 µC/kg.
Frequently asked questions
How do I convert sieverts to rem?+
Multiply sieverts by 100: 1 Sv = 100 rem, 1 mSv = 100 mrem and 1 µSv = 0.1 mrem. To go from rem to sieverts, divide by 100.
What is the difference between gray and sievert?+
The gray measures energy absorbed per kilogram. The sievert adjusts that for the type of radiation and the tissues exposed, to reflect biological risk. For gamma rays and X-rays 1 Gy ≈ 1 Sv; for alpha particles 1 Gy counts as 20 Sv.
How many becquerels are in a curie?+
One curie equals exactly 3.7 × 10¹⁰ becquerels (37 GBq). Radon in homes is often quoted in picocuries per litre; 1 pCi/L equals 37 Bq/m³.
Can I convert becquerels to sieverts?+
Not with a simple factor. The dose from a source depends on the isotope, the radiation it emits, whether it is inhaled, swallowed or external, and for how long. Dose coefficients from radiation protection bodies are needed.
How much radiation does a person get in a year?+
The US NRC estimates the average American receives about 620 mrem (6.2 mSv) per year, roughly half from natural background (mostly radon) and half from man-made sources, almost all of it medical imaging and procedures.