Radiation Dose Converter (sievert, rem, mSv)

Understanding the radiation dose converter — concept and principle

This converter changes radiation dose values between sieverts (Sv), millisieverts (mSv), microsieverts (µSv), rem and millirem. You meet these units in medical imaging reports, dosimeter readings, airport and flight dose estimates, and news about nuclear facilities; older US documents use rem, while most of the world uses sieverts.

How it is calculated

The value is turned into millisieverts and then divided by the size of the target unit. The factors are exact: 1 Sv = 1,000 mSv = 1,000,000 µSv, and 1 rem = 0.01 Sv = 10 mSv, so 1 mSv = 100 millirem. In short, sieverts × 100 = rem.

The principle

The sievert measures equivalent dose and effective dose, which estimate biological harm rather than raw energy. The physical starting point is the absorbed dose in grays (1 Gy = 1 J of energy absorbed per kg). Equivalent dose multiplies it by a radiation weighting factor: 1 for X-rays, gamma rays and electrons, and 20 for alpha particles, because densely ionising radiation damages tissue more. Effective dose then adds up the equivalent doses of the organs, each multiplied by a tissue weighting factor, giving one number that represents whole-body stochastic risk. The rem ("roentgen equivalent man") is the older unit of the same quantity, linked to the rad (0.01 Gy) in the same way.

Worked example

Default inputs: 1 millisievert converted to sieverts.

1. 1 mSv is already in the base unit: 1 mSv.
2. Divide by the size of a sievert, 1,000 mSv: 1 ÷ 1,000 = 0.001.
3. Result: 1 mSv = 0.001 Sv. It is also 1,000 µSv, 0.1 rem and 100 millirem.

How to read the result

For orientation, the worldwide average natural background dose is about 2.4 mSv per year (UNSCEAR). A chest X-ray is roughly 0.02–0.1 mSv. ICRP recommends a limit of 1 mSv per year for members of the public from planned sources, excluding natural background and medical exposure, and 20 mSv per year averaged over five years for workers. Dose rates are often given in µSv/h; multiply by 8.766 to estimate mSv per year if the rate stayed constant all year.

Common mistakes

• Confusing mSv with µSv; the difference is a factor of 1,000.
• Mixing up dose (Sv) with dose rate (Sv per hour).
• Treating sieverts and grays as interchangeable for alpha radiation or very high doses; the weighting factors matter.
• Reading 1 rem as 1 mSv; 1 rem is 10 mSv.

FAQ

Frequently asked questions

How many millirem is 1 mSv?

1 mSv = 100 mrem, and 1 mrem = 0.01 mSv.

How do I convert µSv/h to mSv per year?

Multiply by 8,766 hours and divide by 1,000, that is, multiply by 8.766.

Is gray the same as sievert?

Both are J/kg, but the gray is absorbed energy and the sievert is weighted for biological effect. For X-rays and gamma rays the numbers are equal.

Sources: ICRP Publication 103 (2007), The 2007 Recommendations of the International Commission on Radiological Protection · UNSCEAR 2008 Report, Sources and Effects of Ionizing Radiation · BIPM, The International System of Units (SI Brochure), 9th edition, 2019