Publication Number: FHWA-SA-98-022
Date: May 1998

Moving to Metric 25 mm by 25 mm (Inch by Inch)

Most highway engineers and contractors have gotten used to working with metric measurements, prompted in large part by the switch to metric specifications in Federal-aid construction contracts. Many of the rest of us, however, are still adjusting to the metric system (officially known as the International System of Units, or SI).

That's why articles in Focus contain both metric units and English (inch-pound) units. Although including metric and English units in a story can sometimes be a bit cumbersome, we do so to help familiarize Focus readers with metric equivalents to common English measurements.

Beginning with this issue of Focus, the metric measurement will always be listed first, with the English units in parentheses. In time, we will drop the English units altogether.

To convert from one system to another, we follow the guidelines in IEEE/ASTM SI-10, Standard for Use of the International System of Units (SI): The Modern Metric System (which replaced E380, Standard for Metric Practice). The report is available from the American Society of Testing and Materials (telephone: 610-832-9585; fax: 610-832-9555).

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