What does 49 CFR 171.10 (Units of measure) require?

Short answer

49 CFR 171.10 requires the use of the International System of Units (SI or metric) for most units of measure, with U.S. standard or customary units provided for information only.

The rule says

"Most units of measure in this subchapter are expressed using the International System of Units (SI or metric)." (49 CFR 171.10(a))

"U.S. standard or customary units, which appear in parentheses following the SI units, are for information only and are not intended to be the regulatory standard." (49 CFR 171.10(a))

In plain English

This means that when working with regulations under this subchapter, metric units are the standard, and any U.S. customary units provided are just for reference. In practice, this ensures compatibility with international transportation standards.

What to do

• Use metric units (SI) for all measurements under this subchapter.
• Refer to U.S. customary units only for informational purposes.
• Ensure all documentation and communications use the correct units to maintain consistency and compliance.