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Course Measurement and Certification Procedures

APPENDIX E - Metric-Imperial Conversions

It should be kept in mind that the metric system is the fundamental measurement system of the United States. Since 1893, all U.S. Customary units (also often referred to as “Imperial” or “English” units—see additional info below) have been defined in terms of metric units. The easiest such definition to remember is that of the inch:

one inch = 2.54 centimeters exactly*

*Throughout this appendix, all conversion values in boldface are exact.

From the above, one can derive the equivalents of other units of length, e.g.:

one foot = 12 x 2.54 cm = 30.48 cm = 0.3048 meters
one yard = 3 x 30.48 cm = 91.44 cm = 0.9144 meters
one mile = 5280 x 0.3048 m = 1609.344 m = 1.609344 km

Doing Conversions in the Working Constant

If both mile and kilometer distances must be marked when laying out a race course, the conversion is most easily done in the working constant:

  1. Determine the working constant in counts/km or counts/mile.
  2. Multiply the constant in counts/km by 1.609344 to obtain the constant in counts/mile, or:
  3. Divide the constant in counts/mile by 1.609344 to obtain the constant in counts/km.

Conversion Table for Standard Distances

The following table shows how kilometer and mile distances are related but is not intended for routine measuring. It is much easier to do the conversion once in your measuring constant, as described above, than to do repeated conversions for each split. The table does show, for example, that 10 km is not exactly 6.2 miles. Courses measured to exactly 6.2 miles will not be certified as 10 kilometers!

1 km = 0.62137119 miles
5 km = 3.1068560 miles
8 km = 4.9709695 miles
10 km = 6.2137119 miles
12 km = 7.4564543 miles
15 km = 9.3205679 miles
20 km = 12.427424 miles
25 km = 15.534280 miles
30 km = 18.641136 miles
50 km = 31.068560 miles
60 km = 37.282272 miles
100 km = 62.137119 miles
150 km = 93.205679 miles
200 km = 124.27424 miles
1 mile = 1.609344 km
5 miles = 8.04672 km
10 miles = 16.09344 km
20 miles = 32.18688 km
30 miles = 48.28032 km
40 miles = 64.37376 km
50 miles = 80.4672 km
100 miles = 160.9344 km
half marathon = 21.0975 km = 13.10938 miles
marathon** = 42.195 km = 26.21876 miles

**The marathon is defined as 42.195 km exactly.

Conversions for Steel Taping

1 foot = 0.3048 meters
300 meters = 984.25 feet
1 kilometer = 3280.84 feet
degrees Celsius (°C) = [degrees Fahrenheit (°F) - 32] ÷ 1.8
1 pound-force = 4.448 newtons

More about U.S. Customary, “Imperial” and “English” Units

There is no really good name for the ‘system’ (such as it is) of non-metric units still used in the United States. They aren’t necessarily customary, or used in England, and differ in significant ways from the British Imperial System. In some contexts, they’re referred to simply as “inch-pound” units. The Imperial System is a reasonably well-defined set of units, established by the U.K. in 1824, sharing the same basic units of length and mass as U.S. customary units, but with significantly different sizes for some units such as the gallon, bushel, fluid ounce, and hundredweight.

Of perhaps greater interest to course measurers, two sets of sizes for the non-metric length units (inch, foot, mile, etc.) can still be found in the U.S. The definition quoted above (that 1 inch = 2.54 cm exactly) is the modern definition of the inch, as standardized in 1959 by all English-speaking countries. However, when U.S. customary units were first defined in terms of metric units in 1893, the inch was defined as the fraction 1 / 39.37 of a meter, equivalent to about 2.54000508... centimeters, or about 2 parts per million longer than the modern 2.54 cm definition. Moreover, versions of the foot and mile based on the 1893 U.S. definitions have persisted under the names “U.S. survey foot” and “U.S. survey mile.” Thus, a U.S. survey mile is about 1.609347 km, or about 3 mm longer than a standard mile of exactly 1.609344 km.

Fortunately, the differences between these values are so small (about 8 cm in a marathon) that they are insignificant compared with all the other uncertainties in measuring a race course. We recommend that all length conversions be performed using factors based on the modern definition, 1 inch = 2.54 cm exactly.

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