What is a curie (Ci)?

A curie is a non-SI unit of radioactivity equal to 3.7 × 10^10 disintegrations per second, originally defined as the activity of 1 gram of radium-226. It is commonly used in nuclear medicine and older radiation literature.

What is a becquerel (Bq)?

A becquerel is the SI unit of radioactivity, equal to one disintegration per second. Because the curie is also a unit of activity, curies convert exactly to becquerels: 1 Ci = 3.7 × 10^10 Bq, or 37 GBq.

Can you directly convert curies to grays?

No. A curie measures the activity (decays per second) of a source, while a gray measures the energy a target material absorbs (1 Gy = 1 J/kg). They are different physical quantities. To get a dose in grays you also need the energy per disintegration, the absorbing mass, the exposure time, and the geometry — none of which are fixed by the activity alone. So this tool converts curies to becquerels, the exact and well-defined activity conversion. If you actually need a dose estimate, use the Radiation Dose Rate Calculator (/tool/dose-rate-calculator) or the Activity to Dose Converter (/tool/activity-to-dose), which take those extra factors into account.

What are common curie prefixes?

Common prefixes are: MCi (megacurie, 10^6 Ci), kCi (kilocurie, 10^3 Ci), Ci (curie, base unit), mCi (millicurie, 10^-3 Ci), uCi (microcurie, 10^-6 Ci), and nCi (nanocurie, 10^-9 Ci). Medical applications most often use mCi and uCi.

What is the conversion factor from Ci to Bq?

The conversion is exact: 1 Ci = 3.7 × 10^10 Bq. Multiply the curie value by 3.7 × 10^10 to get becquerels, or divide becquerels by 3.7 × 10^10 to get curies.

Which industries use both curies and becquerels?

Nuclear medicine (PET, SPECT, brachytherapy), radiation oncology, health physics, nuclear power plant safety, and industrial radiography all measure source activity. The curie is common in North American legacy documents; the becquerel is the current SI standard worldwide.

What is 1 curie equal to?

One curie (Ci) equals 3.7 × 10^10 disintegrations per second, which is 37 gigabecquerel (GBq) in SI units. It was originally the activity of 1 gram of radium-226.

Curie to Gray (Ci to Bq) Radioactivity Converter

Name: Curie to Gray (Ci to Bq) Radioactivity Converter
Availability: InStock
Author: Nham Vu

Curie measures radioactivity and gray measures absorbed dose, so there is no fixed Ci-to-Gy factor. Enter a value in curies (any prefix) to get the exact activity in becquerels (1 Ci = 3.7 x 10^10 Bq); for an actual dose estimate, use the linked Dose Rate Calculator or Activity to Dose Converter.

Curie and gray measure different things — you can't convert between them with a fixed number.

Curie (Ci) measures radioactivity (decays per second). Gray (Gy) measures absorbed dose (energy absorbed per kilogram). Absorbed dose depends on the radionuclide's emission energy, distance, exposure time, and the absorbing mass — none of which are fixed by the activity alone. This page converts Curie ↔ Becquerel (the exact activity conversion: 1 Ci = 3.7 × 10¹⁰ Bq). To estimate actual dose, use the calculators below.

Radiation Dose Rate Calculator Activity to Dose Converter

Curie to Becquerel Converter

Curie Prefix

Radioactivity Value

Common Activity Reference Points

Click a row to load it

Context	Input (Ci)	Result (Bq)

Summary

How it works

Select the curie prefix (Ci, mCi, uCi, nCi, kCi, or MCi) from the dropdown.
Enter the radioactivity value in the input field.
The equivalent activity in becquerels appears instantly in the result panel.
The conversion formula is shown below the inputs for reference.
Browse the reference table for common source-activity benchmarks.
Click any reference row to load that value into the converter.

Use cases

Convert isotope activity measurements for medical dosimetry calculations.
Cross-reference radiation safety thresholds in different unit systems.
Verify source-activity figures in nuclear medicine or radiation therapy.
Study or teach radiation physics unit conversions.
Convert published research data from curies to SI becquerel units.
Check equipment calibration values across legacy and modern unit systems.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu