# Conversion Table

Canada and much of the world uses units from the Système 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
• 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
Système International
Système International
to Old system

Table 1 footnotes

Table 1 footnote 1

1 Bq = 1s-1

The becquerel (Bq) replaces the curie (Ci).Table 1 footnote *
• 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 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)

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).

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.