Convert Curies to Millicuries
Curie (Ci) to Millicurie (mCi) radioactivity conversion — enter any value below to get an instant result, or use the table for common values.
Results from this calculator are estimates provided for general informational purposes only, based on formulas, rates, and standards commonly accepted as of 2026. Figures may differ slightly from other calculators or professional sources due to rounding methods, differing assumptions, or regional regulations, and rules may change over time. Always consult a qualified professional — such as a financial advisor, healthcare provider, or other relevant specialist — before making decisions based on these results.
Result
1 Ci = 1000 mCi
1 Curie = 1000 Millicuries
1 Millicurie = 0.001 Curies
1 Ci in every supported unit
Conversion chart: Curie to Millicuries
Conversion table
| Curie (Ci) | Millicurie (mCi) |
|---|---|
| 0.01 Ci | 10 mCi |
| 0.1 Ci | 100 mCi |
| 1 Ci | 1000 mCi |
| 2 Ci | 2000 mCi |
| 3 Ci | 3000 mCi |
| 5 Ci | 5000 mCi |
| 10 Ci | 10000 mCi |
| 20 Ci | 20000 mCi |
| 50 Ci | 50000 mCi |
| 100 Ci | 100000 mCi |
| 1000 Ci | 1000000 mCi |
Curie (Ci)
Definition: The older, much larger CGS-derived unit of activity, originally defined as the activity of exactly one gram of radium-226 — equal to 37 billion decays per second.
History: Named after Marie and Pierre Curie in recognition of their pioneering research into radioactivity (including the discovery of polonium and radium), the curie was the standard unit of activity for most of the 20th century before the SI adopted the becquerel in 1975.
Current use: Still widely used in US medical, industrial, and regulatory contexts (often as milli- or microcuries) even though most of the rest of the world has moved to becquerel — because a curie is such an enormous number of decays per second, real-world sources are almost always quoted as a fraction of one.
Millicurie (mCi)
Definition: An SI-prefixed submultiple of the curie equal to one thousandth of a curie (37 million decays per second), the most common scale for therapeutic nuclear-medicine doses.
History: It follows the curie's historical origin, scaled down by the standard milli- prefix as clinical radiopharmaceutical doses turned out to sit well below a full curie.
Current use: The standard unit for prescribing therapeutic radioisotope doses in nuclear medicine, such as iodine-131 treatments for thyroid conditions, in US clinical practice.
Supported Units
| Unit | Symbol | In Bq |
|---|---|---|
| Becquerel | Bq | 1 Bq |
| Terabecquerel | TBq | 1E+12 Bq |
| Gigabecquerel | GBq | 1E+09 Bq |
| Megabecquerel | MBq | 1000000 Bq |
| Kilobecquerel | kBq | 1000 Bq |
| Millibecquerel | mBq | 0.001 Bq |
| Curie | Ci | 3.7E+10 Bq |
| Kilocurie | kCi | 3.7E+13 Bq |
| Millicurie | mCi | 37000000 Bq |
| Microcurie | µCi | 37000 Bq |
| Nanocurie | nCi | 37 Bq |
| Picocurie | pCi | 0.037 Bq |
| Rutherford | Rd | 1000000 Bq |
| One/Second | 1/s | 1 Bq |
| Disintegrations/Second | dis/s | 1 Bq |
| Disintegrations/Minute | dis/min | 0.016666667 Bq |
About These Parameters
- Value
- The activity you want to convert, expressed in the "From" unit. Accepts decimals, and can represent anything from a trace laboratory tracer in nanocuries to an industrial gamma-radiography source in terabecquerels.
- From Unit
- The unit your activity figure is currently measured in — a nuclear-medicine dose sheet's millicuries, an environmental report's becquerels per kilogram, or an older physics text's rutherfords.
- To Unit
- The unit you want the result converted into. Use the swap button to flip From and To instantly, which is handy when translating a US clinical curie figure into the modern SI becquerel or vice versa.
How Radioactivity Conversion Works
The Formula
Every unit here is defined by a fixed multiplier relative to the becquerel. To convert a value from one unit to another:
result = value × (factor of "From" unit ÷ factor of "To" unit)
For Curie → Millicurie: multiply by 1000. For example, 1 Ci × 1000 = 1000 mCi.
Why the Curie Is Still Everywhere Despite Becquerel Being the SI Standard
The curie was defined in the early 20th century as the activity of exactly one gram of radium-226 — a huge number of decays per second (37 billion) that happened to match the quantities researchers were actually handling at the time. When the SI adopted the becquerel in 1975 as a deliberately small, easy-to-reason-about unit (one decay per second), it created a scale mismatch: real sources that were "1 curie" became "37 billion becquerel," an awkward number to say or write. US medical and industrial practice never fully switched over, which is why millicuries and microcuries still dominate American clinical paperwork even as the rest of the world reports in kilobecquerels and megabecquerels.
Activity Is Not the Same as Dose
A source's activity tells you how many atoms are decaying every second, but says nothing about how much of that radiation actually reaches and is absorbed by a person or object — that depends on distance (radiation intensity falls off with distance), shielding, and the type of radiation being emitted (alpha particles barely penetrate skin; gamma rays pass through substantial shielding). A one-curie source sealed behind thick lead delivers a far lower dose rate than the same source held in an open hand. That's why radiation-safety training treats activity and dose rate as two separate numbers that must both be known, never one inferred from the other.
Example
An activity of 1 Ci equals 1000 mCi. For scale, a typical nuclear-medicine diagnostic dose is a few hundred megabecquerels (roughly 10-30 millicuries), household smoke detectors contain an americium-241 source of about 1 microcurie (37,000 becquerels), and industrial radiography sources used for inspecting welds commonly run several terabecquerels (tens to hundreds of curies).
Frequently Asked Questions
How many Millicuries are in 1 Curie?
1 Curie (Ci) equals exactly 1000 Millicuries (mCi).
What's the difference between a becquerel and a curie?
Both measure activity (decays per second), but on very different scales. One becquerel is exactly one decay per second; one curie is 37 billion decays per second — the activity originally defined as one gram of radium-226. Because the curie is so large, real sources are usually quoted in millicuries or microcuries, while becquerel figures are more often scaled up with mega- or giga- prefixes.
Does higher activity always mean higher radiation exposure?
Not necessarily. Activity only describes the source's own decay rate — the actual dose someone receives also depends on distance from the source, shielding in between, exposure time, and the type of radiation emitted. A highly active but well-shielded or distant source can deliver a lower dose rate than a much less active source held close by. See the separate Radiation Converter for dose rate specifically.
What is the rutherford and why isn't it used anymore?
The rutherford, named after physicist Ernest Rutherford, was a mid-20th-century unit equal to one million decays per second — a middle ground between becquerel and curie. It never gained wide international adoption and was effectively abandoned once the SI standardized on the becquerel in 1975, so it now appears only in older physics literature.
Why are disintegrations/minute used instead of disintegrations/second in some labs?
Liquid-scintillation counters and similar laboratory instruments historically reported raw counts on a per-minute basis, matching typical counting-run durations, so biochemistry and radiochemistry labs still commonly report activity in disintegrations (or counts) per minute rather than converting to the SI per-second convention.