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Environmental and Workplace Health

Conversion Table

Canada and much of the world uses units from the Systme International (SI) to measure radiation. The SI is based on the metric system. These units include the:

  • becquerel
  • gray
  • sievert
  • coulomb/kg

From the early 1900s, through to the 30s, until the 1960s, another set of units were used. They were called the:

  • curie
  • rad
  • rem
  • Roentgen

The United States still uses these units. You may also find them in older documents.

This table shows a simple comparison between the words used in the SI and the old system.
Old system to
Systme International
Systme International
to Old system

Table 1 footnotes

Table 1 footnote 1

1 Bq = 1s-1

Return to table 1 footnote * referrer

The becquerel (Bq) replaces the curie (Ci).*
  • 1 kilocurie (kCi) = 37 terabecquerel (TBq)
  • 1 curie (Ci) = 37 gigabecquerel (GBq)
  • 1 millicurie (mCi) = 37 megabecquerel (MBq)
  • 1 microcurie (µCi) = 37 kilobecquerel (kBq)
  • 1 nanocurie (nCi) = 37 becquerel (Bq)
  • 1 picocurie (pCi) = 37 millibecquerel (mBq)
The becquerel (Bq)Table 1 footnote * replaces the curie (Ci).
  • 1 terabecquerel (TBq) ~ 27 curie (Ci)
  • 1 gigabecquerel (GBq) ~ 27 millicurie (mCi)
  • 1 megabecquerel (MBq) ~ 27 microcurie (µCi)
  • 1 kilobecquerel (kBq) ~ 27 nanocurie (nCi)
  • 1 becquerel (Bq) ~ 27 picocurie (pCi)
The gray (Gy) replaces the rad (rad).
  • 1 kilorad (krad) = 10 gray (Gy)
  • 1 rad (rad) = 10 milligray (mGy)
  • 1 millirad (mrad) = 10 microgray (µGy)
  • 1 microrad (µrad) = 10 nanogray (nGy)
The gray (Gy) replaces the rad (rad).
  • 1 gray (Gy) =100 rad (rad)
  • 1 milligray (mGy) = 100 millirad (mrad)
  • 1 microgray (µGy) = 100 microrad (µrad)
  • 1 nanogray (nGy) = 100 nanorad (nrad)
The coulomb/kg (C/kg) replaces the roentgen (R).
  • 1 kiloroentgen (kR) ~ 258 millicoulomb/kg (mC/kg)
  • 1 roentgen (R) ~ 258 microcoulomb/kg (µC/kg)
  • 1 milliroentgen (mR) ~ 258 nanocoulomb/kg (nC/kg)
  • 1 microroentgen (µR) ~ 258 picocoulomb/kg (pC/kg)
The coulomb/kg (C/kg) replaces the roentgen (R).
  • 1 coulomb/kg (C/kg) ~ 3876 roentgen (R)
  • 1 millicoulomb/kg (mC/kg) ~ 3876 milliroentgen (mR)
  • 1 microcoulomb/kg (µC/kg) ~ 3876 microroentgen (µR)
  • 1 nanocoulomb/kg (nC/kg) ~ 3876 nanoroentgen (nR)
The sievert (Sv) replaces the rem (rem).
  • 1 kilorem (krem) = 10 sievert (Sv)
  • 1 rem (rem) = 10 millisievert (mSv)
  • 1 millirem (mrem) = 10 microsievert (µSv)
  • 1 microrem (µrem) = 10 nanosievert (nSv)
The sievert (Sv) replaces the rem (rem).
  • 1 sievert (Sv) = 100 rem (rem)
  • 1 millisievert (mSv) = 100 millirem (mrem)
  • 1 microsievert (µSv) = 100 microrem (µrem)
  • 1 nanosievert (nSv) = 100 nanorem (nrem)

About the becquerel

The becquerel (Bq) is named after the French physicist A.H. Becquerel. This unit measures radioactivity in a substance. It doesn't consider the type of radiation emitted or what its effects may be. One becquerel equals one nuclear disintegration per second. This is a very small unit, so multiples are often used. These include the:

  • kilobecquerel (kBq: thousand Bq);
  • megabecquerel (MBq: million Bq); and
  • gigabecquerel (GBq: thousand million or billion Bq).

About the gray

The gray (Gy) was defined in 1975 in honor of English radiobiologist Louis H. Gray (1905-1965). This unit describes how much energy is absorbed by a substance from the radiation passing through it, or the absorbed dose. One gray corresponds to one joule of radiation energy absorbed by one kilogram of matter. Measuring how many grays a substance receives in one hour tells us what the rate is. The gray is a very large dose of radiation. A more useful unit is the milligray (mGv). This is one-thousandth of a gray.

About the sievert

The sievert (Sv) is named after the Swedish physicist Rolf M. Sievert. The unit reflects the biological effects of the ionizing radiation absorbed. It is used to express both the equivalent dose and the effective dose. The sievert is a very large dose of radiation. A more useful unit is the millisievert (mSv). This is one-thousandth of a sievert.