Lesson 12: Introduction to SI Units
The purpose of this module is to review the relationship between the International System of Units and
the customary units for radiological measurement.
Upon completion of this lesson, you will be able to:
Describe the relationships between the International System of Units (SI Units) and the
customary units for radiological measurements.
Convert from SI to customary units and customary units to SI using a hand calculator.
Remember you can access the glossary in one of two ways throughout this course. You can select the
glossary button in the top right hand corner of each main content screen. In addition, on content
screens you can select underlined words to access their definitions in the online glossary. Selecting an
underlined word will take you directly to its definition in the glossary.
This lesson should take approximately 1 hour to complete.
Introduction to SI Units
The transition to measurement using the International System of Units, or SI, which stands for Systeme
International d’Unites, is required by Presidential Executive Order 12770 and Public Laws 94-168 and
To ensure a smooth transition to SI units, international and domestic organizations have begun showing
information on packages and shipping documents in both the SI and customary units.
Many sources of information use customary units, such as the Curie, and others use SI units, such as the
Becquerel. Going from one measurement to another requires the use of a conversion factor, which
you’ll learn more about later in this lesson.
Before moving on to measurement conversions, let’s review the metric prefixes used to more easily
express measured values.
Since very large and very small numbers are used in quantifying radioactive materials, it is necessary to
use numerical abbreviations to write the measured values in a practical way. The most common units
used in measurements to describe radiation characteristics are:
kilo (k) = 10 x 103
milli (m) = 10 x 10-3
micro (µ) = 10 x 10-6
nano (n) = 10 x 10-9