Radioactivity Converter
Convert radioactive activity between Bq, kBq, MBq, GBq, Ci, mCi, and µCi. Enter an activity value, then choose the starting and target units.
Convert Radioactivity Between Units
Radioactivity Formula
Where:
- \(A_{\mathrm{from}}\) — the entered activity in the starting unit
- \(A_{\mathrm{to}}\) — the converted activity in the target unit
- \(f_{\mathrm{from}}\) — the number of becquerels in one starting unit
- \(f_{\mathrm{to}}\) — the number of becquerels in one target unit
The converter first expresses the entered activity in becquerels, then divides by the becquerel value of the target unit. One becquerel is one nuclear decay per second.
Radioactivity – Calculation Example
Example: enter the default Activity value of 1, then select Curie (Ci) as the From unit and Becquerel (Bq) as the To unit.
\[ A_{\mathrm{to}}=1\,\mathrm{Ci}\times\frac{3.7\times10^{10}\,\mathrm{Bq}}{1\,\mathrm{Ci}}=3.7\times10^{10}\,\mathrm{Bq} \]
Result: 1 Ci = 37,000,000,000 Bq.
How to use the calculator
- Enter a nonnegative number in Activity value. For example, enter 1 to convert one unit, or enter a measured activity to convert that reading.
- Choose the unit of that number in From unit.
- Choose the unit you need in To unit.
- Read Converted Radioactivity. Its unit is the one selected in To unit.
You can select the same unit in both menus to leave the value unchanged. The available units are Bq, kBq, MBq, GBq, Ci, mCi, and µCi. The calculator does not accept negative activity values.
What radioactive activity measures
Radioactive activity is the rate at which unstable nuclei decay. A source with an activity of 1 Bq has, on average, one nuclear decay per second; 1,000 Bq is 1 kBq. Individual decays occur unpredictably, so activity describes an average rate rather than a promise that exactly that many decays will occur in every second.
The becquerel is the SI unit of activity. The curie is an older, much larger unit: 1 Ci is exactly \(3.7\times10^{10}\) Bq for unit conversion. Its subdivisions are useful for smaller activities: 1 mCi is \(3.7\times10^7\) Bq, and 1 µCi is \(3.7\times10^4\) Bq. These conversions change only the unit, not the quantity of radioactive material or its decay rate.
Activity appears on radioactive source labels and in laboratory, medical, and environmental measurements. It is not a radiation dose. Two sources with the same activity can produce different exposures because the radiation type and energy, shielding, distance, and duration differ. Activity alone therefore cannot tell you whether a source is safe or calculate a dose in sieverts.
Becquerels and hertz both have units of reciprocal seconds, but they describe different things: Bq counts nuclear decays, while Hz describes the repetition rate of a periodic event. For periodic rates rather than radioactive activity, use the frequency converter.
Conversion factors
Each factor below gives the number of becquerels in one unit. Multiply by the factor to convert to Bq; divide by the factor to convert from Bq.
| Unit | Equivalent in Bq |
|---|---|
| 1 Bq | 1 Bq |
| 1 kBq | 1,000 Bq |
| 1 MBq | 1,000,000 Bq |
| 1 GBq | 1,000,000,000 Bq |
| 1 Ci | 37,000,000,000 Bq |
| 1 mCi | 37,000,000 Bq |
| 1 µCi | 37,000 Bq |
Assumptions and practical limits
This is a unit conversion, not a decay-over-time calculation. It assumes the activity being converted refers to the same source at the same time. A radioactive source’s activity changes over time according to its half-life, but this converter does not ask for an isotope, a half-life, or an elapsed time.
The result is rounded to 10 decimal places. When converting a small Bq value to Ci, the displayed result may be 0 Ci even though the activity is not zero. For example, 1 Bq is approximately \(2.7027\times10^{-11}\) Ci. Choose a smaller target unit, such as µCi, when you need a more useful displayed value.
The calculator converts total activity, not activity concentration such as Bq per kilogram or Bq per liter. If you are working with a moving material stream, mass flow rate is a separate measurement; converting either measurement does not determine the other. Likewise, an instrument’s detected counts per second may differ from the source’s decays per second because detection efficiency, geometry, and background affect the count rate.
Frequently Asked Questions
How do I convert between becquerels and curies by hand?
Use the conversion factor as a fraction so the starting unit cancels. For example, to convert 74 MBq to mCi, first write 74 MBq as 74,000,000 Bq, then divide by 37,000,000 Bq per mCi. The result is 2 mCi. To reverse the conversion, multiply the mCi value by 37,000,000.
What is a normal or safe radioactivity level in Bq?
There is no single safe activity value. The significance of a reading depends on the radionuclide, whether the material is sealed or could enter the body, the radiation it emits, and the exposure conditions. A Bq value alone cannot establish risk. For a source, sample, or workplace reading, use the applicable safety limits and seek advice from a qualified radiation-safety professional.
How do I convert decays per minute to becquerels?
Divide decays per minute (dpm) by 60 to get becquerels, because a becquerel represents one decay per second. For example, 6,000 dpm equals 100 Bq. Conversely, multiply Bq by 60 to get dpm. This works for actual decay rates; an instrument’s counts per minute may be lower because it does not detect every decay.
Can I convert a detector reading in counts per second directly to Bq?
Not reliably without knowing how the measurement was made. Counts per second (cps) records detected events, while Bq describes decays in the source. If the background-subtracted count rate is 200 cps and the overall detection efficiency for that setup is 25%, an estimated activity is \(200/0.25=800\) Bq. The estimate depends on the detector, source geometry, and radiation type.
How do I find a source’s activity after several half-lives?
Multiply its initial activity by \((1/2)^n\), where \(n\) is the number of half-lives elapsed. After three half-lives, a 400 MBq source has an activity of 50 MBq. For a time that is not a whole number of half-lives, use \(A=A_0(1/2)^{t/T_{1/2}}\). You need the radionuclide’s half-life and a clearly stated starting time.
How do I convert activity concentration into total activity?
Multiply the concentration by the amount of material, using matching units. For example, 15 Bq/L in 4 L of liquid gives a total activity of 60 Bq, assuming the concentration is representative throughout the liquid. Likewise, Bq/kg multiplied by kilograms gives Bq. Converting the concentration’s activity unit alone does not account for sample volume or mass.