Curie (Ci)
The curie (Ci) is the traditional unit of radioactivity, defined as exactly 3.7 × 10¹⁰ becquerels, close to the activity of one gram of radium-226. It is still used in the United States.
Symbol: Ci
Quantity: activity of a radioactive source
SI relation: 1 Ci = 37000000000 Bq (exact)
Derivation: 1 Ci = 3.7 × 10¹⁰ Bq exactly (originally the activity of 1 g of radium-226).
Exact: yes, by definition
Typical uses
- US nuclear regulation and licences
- Sealed source labels
- Older literature
Convert curies to other units
| Conversion | 1 Ci equals | Reverse |
|---|---|---|
| curie to becquerel | 37000000000 Bq | becquerel to curie |
| curie to megabecquerel | 37000 MBq | megabecquerel to curie |
| curie to millicurie | 1000 mCi | millicurie to curie |
| curie to picocurie | 1000000000000 pCi | picocurie to curie |
| curie to kilobecquerel | 37000000 kBq | kilobecquerel to curie |
| curie to gigabecquerel | 37 GBq | gigabecquerel to curie |
| curie to microcurie | 1000000 µCi | microcurie to curie |
| curie to disintegration per minute | 2220000000000 dpm | disintegration per minute to curie |
| curie to terabecquerel | 0.037 TBq | terabecquerel to curie |
| curie to nanocurie | 1000000000 nCi | nanocurie to curie |
| curie to rutherford | 37000 Rd | rutherford to curie |
Open the Radioactivity Converter to convert any value between all units.
Sources
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "curie".
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). Curie (Ci). Retrieved October 25, 2026, from https://scientificconverters.com/units/curie/
IEEE
Scientific Converters, "Curie (Ci)," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/units/curie/