Radioactivity Conversion Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/10/2026
To convert a radioactive activity, it is reduced to the becquerel (the SI unit), then converted into the new unit. 1 curie equals exactly 37 billion becquerels (3.7×10¹⁰ Bq).
Explanation
Radioactive activity measures the number of nuclear disintegrations occurring each second in a quantity of radioactive matter. The becquerel (Bq), the SI unit, corresponds to exactly one disintegration per second — a unit so small that it gives astronomical numbers as soon as it is applied to radioactive sources in common use, hence the usefulness of the curie (Ci) and its submultiples. The curie, named in honor of Pierre and Marie Curie, was historically defined as the approximate activity of one gram of radium-226; it is now fixed by an exact definition at 3.7×10¹⁰ Bq, independent of any physical measurement of radium itself. The millicurie (one thousandth of a curie) remains commonly used in nuclear medicine to express the doses of radioactive tracers administered during imaging exams (scintigraphy, PET scan), whose gradual elimination from the body follows a decay described by our drug half-life calculator, while the microcurie is used for smaller quantities, for example in laboratory research. Although the becquerel has been the official SI unit since 1975, the curie remains very widely used in North American clinical and industrial practice and in many historical technical documents, which makes this conversion frequently necessary to compare sources documented in different units.
Example: converting 1 curie to becquerels
Inputs
Value: 1. Starting unit: curie. Target unit: becquerel.
Calculation
1 Ci × 3.7×10¹⁰ Bq per Ci = 3.7×10¹⁰ Bq.
Result
1 curie equals exactly 37,000,000,000 becquerels.
Frequently asked questions
Why is the curie exactly 3.7×10¹⁰ Bq?
This value comes from the historical definition of the curie as the activity of one gram of radium-226, measured at the time it was created. Rather than keeping a measured value subject to revision as later, more precise measurements of radium were made, the scientific community fixed this value as an exact definition of the curie, which makes it today a fixed conversion rather than an approximation.
Why is the curie still used when the becquerel is the official unit?
The becquerel has been the legal SI unit since 1975, but the curie remains deeply entrenched in some historical practices, particularly in North American nuclear medicine and in much of the scientific and technical literature published before that date. This dual presence is why a reliable conversion between the two systems remains regularly needed.
Does this conversion apply to any type of radioactive radiation?
Yes, the becquerel and the curie measure the ACTIVITY of the source (the number of disintegrations per second), a quantity independent of the type of radiation emitted (alpha, beta, gamma) or its biological hazard. To assess the biological effect of an exposure, other units come into play (the sievert for equivalent dose), which this activity conversion alone does not cover — just as our pressure conversion calculator measures a physical quantity without prejudging its practical effects.