METRIC UNIT CONVENTIONS
The modern metric system, called the ‘‘Système International d’Unités’’ (or the
International System of Units in English), was finalized in its current form by
international agreement in 1960 and is the standard international language of mea-
surement. It has been mandated as the preferred system of measurement in the
United States since the ‘‘Metric Conversion Act’’ was passed by congress in 1975.
This was further enhanced by an Executive Order in 1991 that required all govern-
ment publications to be revised and that a transition plan for conversion be adapted.
All federal government construction, and most states, now require metric units to
be used for their projects, but not much progress has been made in the United
States for total implementation of metric units for material and design used only
in this country.
The United States is the last industrialized country that does not completely use
the Metric system, but rather a system called inch-pound units. This appendix will
provide the most currently accepted means of expressing the various metric mea-
surement units and their abbreviations. They have been obtained from experience
with various code bodies and from vendors who supply equipment to both the
United States and foreign markets. In addition, a limited table of conversion factors
is provided for the most often referred to units used by engineers in the construction
industry. For a complete list of conversion factors, refer to standard engineering
references. The abbreviations used will refer to either IP for the inch-pound units
currently in use in the United States or SI for the International System of Units.
BASIC METRIC FUNDAMENTALS
There are three classes of SI units: base units, derived units, and supplementary
A. Base units consist of seven well-defined units which, by convention, are re-
garded as dimensionally independent. They are:
1. Length................................ meter (m)
2. Mass ................................. kil