It is now the accepted practice in the Industry to use a Metric system based on the International Standard System of Units called "SI" (Système International). This system has now been adopted in the writing of the National and International Standards for all issues concerning fans and air performance. However, there is still enough documentation in use throughout the world for us to have to be aware of Imperial or "I-P" units and one or two other local deviations from the basic SI system. Some conversion factors are given in the following table. Multiply the "Alternate" unit by the conversion factor to obtain the "Preferred" unit.
Units commonly found in Fan or System Performance Specifications:
To avoid using very large or very small numbers, there are "Multiplying Prefixes".
