Hong Life CalculatorsUnderstanding the radioactivity converter — concept and principle
This converter changes radioactivity (activity) between becquerels (Bq, kBq, MBq, GBq) and curies (Ci, mCi, µCi, pCi). Use it for nuclear-medicine doses, laboratory sources, radon test results and older documents that still use curies, when you need to compare them with SI values in becquerels.
How it is calculated
result = value × (Bq per "from" unit) ÷ (Bq per "to" unit)
- 1 Bq = 1 radioactive decay per second.
- 1 Ci = 3.7 × 10¹⁰ Bq = 37 GBq exactly.
- 1 mCi = 37 MBq; 1 µCi = 37 kBq; 1 pCi = 0.037 Bq.
- The SI prefixes k, M and G mean 10³, 10⁶ and 10⁹.
The principle
Activity counts how many atoms in a sample decay each second. The becquerel, the SI unit, is simply one decay per second. The curie is older; it was based on the activity of about one gram of radium-226 and was later fixed by definition at exactly 3.7 × 10¹⁰ decays per second. Because both are fixed counts per second, the conversion is exact. Activity falls over time as the material decays, halving every half-life, so a value always refers to a particular date and time.
Worked example
Default inputs: 1 millicurie to becquerels.
- 1 mCi = 0.001 Ci.
- 0.001 × 3.7 × 10¹⁰ = 37,000,000 Bq.
- That is 37,000 kBq, 37 MBq or 0.037 GBq, and 1,000 µCi or 1,000,000,000 pCi.
How to read the result
Activity tells you how many decays happen, not how much harm they do. The dose to a person depends on the type and energy of the radiation, where the source is, and how long you are exposed; that is measured in grays and sieverts. Radon in indoor air is reported per volume: 1 pCi/L = 37 Bq/m³. The US EPA recommends action at 4 pCi/L (148 Bq/m³), and the WHO suggests a reference level of 100 Bq/m³ where possible.
Common mistakes
- Treating becquerels as a dose. Bq counts decays; Sv describes biological effect.
- Moving a decimal when converting pCi/L to Bq/m³; multiply by 37.
- Ignoring decay. A short-lived medical isotope can lose most of its activity within a day.
- Confusing mCi (milli, 10⁻³) with µCi (micro, 10⁻⁶).
Frequently asked questions
How many becquerels is 1 curie?
3.7 × 10¹⁰ Bq, which is 37 GBq.
How do I convert pCi to Bq?
Multiply by 0.037. For example, 4 pCi is 0.148 Bq.
How many MBq is 1 mCi?
Exactly 37 MBq.
Is a high becquerel value always dangerous?
Not necessarily. Food, soil and the human body all contain natural radioactivity. Risk depends on the radionuclide, the route of exposure and the dose.
Sources: BIPM, The International System of Units (SI Brochure), 9th edition · ICRP Publication 103 (2007), Recommendations of the ICRP · US EPA, A Citizen's Guide to Radon · WHO Handbook on Indoor Radon (2009)