Standard Units

International System of Units — The Metric Measurement System

International System of Units Public Law 94-168, §2 requires use of the International System of Units for measurement in U.S. Government programs, "except where impractical." That requirement is reflected in NASA policy, NPD 7120.4. That measurement system, formally known as the "SI" system," after its name in French, Systeme Internationale, is almost universally used by all countries except the United States. Use of SI measurement is growing in importance for international trade.

Although use of SI in the U.S. is increasing, aerospace is recognized as one area where adoption will be difficult, due to the long-standing use of the U.S.-based "inch-pound" system for aircraft.

Nevertheless, space programs do make significant use of SI, particularly for science measurement, and increasingly for hardware and operations, particularly as international cooperation in space increases.

The Chief Engineer serves as the Metric Executive for NASA to meet the external requirements of 15 U.S.C. §205b and Executive Order 12770.

Non-NASA Resources


The Metric Program Office at the National Institute for Standards and Technology (NIST) serves as the official coordinator for SI transition programs across the Federal government. Two items of particular interest at the NIST site are: