## The "Foot-to-Meter" Conversion

There is some confusion surrounding the correct value to use when converting the English "foot" measurement to the metric "meter" measurement and vice versa. This confusion stems from the fact that there are two, though slightly different, conversion factors that may be used in this process.

### Foot-Meter Conversion Factors

Both values

• 0.304 800 609 6012

and

• 0.3048

are correct factors that can be used for converting feet to meters.

How is it possible to have two values for the same conversion? To gain an understanding of how this is possible, and why it is allowed to continue, it is necessary to take a brief look at the history of the metric system within the United States.

### History

The metric system was developed during the French Revolution in the late 1700's. It was first promoted in the United States by Thomas Jefferson and in 1866 the US Congress officially recognized the metric system as a legal system of units. In 1893, the Office of Weights and Measures (now the National Bureau of Standards), fixed the value of the U.S. "yard" in terms of the meter as follows:

• 1 yard = 3600/3937 meter or 1 yard = 0.914 401 8288 meter

this relation is equivalent to:

• 1 foot = 12/39.37 meter or 1 foot = 0.304 800 609 6012 meter

Unfortunately, other nations used a slightly different conversion factor. To solve this deviation, a refinement was made in the definition of the yard to bring the US yard and the yard used in other countries into agreement. In 1959 the national standards laboratories of the English-speaking nations agreed to standardize the relation between the yard and the meter as follows:

• 1 yard = 0.9144 meter
• 1 foot = 0.3048 meter
• 1 inch = 25.4 millimeter

The new length of yard is shorter by exactly two parts in a million.

At the same time it was decided that any data in feet derived from and published as a result of geodetic surveys within the U.S. would remain with the old standards (1 foot = 12/39.37 meter) pending any further decisions. This foot measurement is called the U.S. Survey foot.

This then, is how we came to have two values for foot-meter conversions. One value, (1 foot = 12/39.37 meter), should be used when converting a measurement that is based on geodetic surveys. The other value, (1 foot = 0.3048 meter), should be used for any other conversions that are not related to geodetic data. Whichever value is used, it should be used consistently throughout that project.