Radiation Units

Features

• Activity: Bq, kBq, MBq, GBq, TBq, Ci, mCi, µCi, nCi
• Absorbed dose: Gy, mGy, µGy, rad, mrad
• Equivalent dose: Sv, mSv, µSv, rem, mrem
• Equivalent dose rate: Sv/h, mSv/h, µSv/h, rem/h, mrem/h — what a Geiger counter reads
• Exposure: C/kg, mC/kg, R, mR
• ⚠️ Converts within one group only, and never produces a cross-group number
• ⚠️ The result explains, group by group, what the other four measure and why they do not convert
• ⚠️ It also names the source of the confusion: under photons Sv = Gy × 1, so the numbers match
• Every in-group conversion rests on defined values (1 Ci = 3.7×10¹⁰ Bq, 1 Gy = 100 rad), so there is no measurement error
• Accepts scientific notation such as `1e-6`, and extreme magnitudes do not collapse into a row of zeros

How to use

1. Choose the input unit — the parentheses say which group it belongs to
2. Enter the value (scientific notation is fine)
3. The result converts within the group and lists why the other groups do not convert

FAQ

Why can’t 1 Bq be converted to Sv?

Because they do not measure the same thing. Bq is how many decays per second the source undergoes; Sv is the biological effect on a body. Getting from one to the other requires the type and energy of the radiation, the distance to the source, any shielding, and the route into the body. None of that is in the number of becquerels, so it cannot yield a sievert. Estimating it takes a dosimetric model, not a conversion factor.

Then why does everyone say 1 Gy = 1 Sv?

Because under photon irradiation (X-rays, gamma) it holds: Sv = Gy × the radiation weighting factor, and for photons and electrons that factor is exactly 1, so the numbers coincide. For neutrons the factor reaches 20, and for alpha particles it is 20. That also only covers the step from absorbed to equivalent dose — between activity and dose there is the whole question of distance and shielding. Used as a general rule, it can be wrong by a factor of tens where accuracy matters.

Which group is the µSv/h on a Geiger counter?

Equivalent dose rate — equivalent dose per hour, so it converts freely with Sv/h, mSv/h and mrem/h. Note that a meter shows a rate, while an annual accumulated dose is that rate times time: 0.2 µSv/h for a year is 1.75 mSv, which is not a number you can compare directly against “one chest X-ray”.

Why is exposure (C/kg, roentgen) its own group?

Because exposure measures the ionisation radiation produces in air and is not itself a dose — it comes from X-ray and gamma dosimetry, which is what could be measured at the time. Going from exposure to absorbed dose requires knowing what material is being irradiated and the photon energy, so it stands alone here. 1 R = 2.58×10⁻⁴ C/kg is a defined value.

How precise are these conversions?

Every in-group conversion is a defined value with no measurement error: 1 Ci = 3.7×10¹⁰ Bq by definition, as are 1 Gy = 100 rad, 1 Sv = 100 rem and 1 R = 2.58×10⁻⁴ C/kg. The last digit here is trustworthy — the uncertainty to watch is in the measurement, not the conversion.