Home - Education Resources - NDT Course Material - Radiography - Real-Time APPENDIX I METRIC CONVERSION All units of length in the metric system are derived from the meter. Although not a commonly used unit of measure in engineering, the meter is included here to show place value. Prefixes to the basic unit denote unit length. For example, the prefix cent- signifies one-hundredth; therefore, one centimeter is one one-hundredth of a meter. kilo =1,000 1 kilometer (km) = 1,000 meters (m) hecto=100 1 hectometer (hm) = 100 m Deca = 10 1 decameter (dam) = 10 m 1 meter (m) = 1 m deci = 0.1 1 decimeter (dm) = 0.1 m centi = 0.01 1 centimeter (cm) = 0.01 m milli = 0.001 1 millimeter (mm) = 0.001 m micro = 0.000001 1 micrometer (micron) = 0.000001 m Conversion between units of length in the metric system involves moving the decimal point to the right or to the left. Listing the units in order from largest to smallest will indicate how many places to move the decimal point and in which direction. To convert 4,200 cm to m, write the metric units in order, from largest to smallest. km hm dam m dm cm mm __ __ micron Because centimeters are two places to the right of meters, converting cm to m requires moving two decimal positions left; therefore, 4,200 cm = 42.00 m. To convert 5.0 microns to mm, list the metric units in order, from largest to smallest. Km hm dam m dm cm mm __ __ micron Because microns are three positions to the right of millimeters, converting micron to mm requires moving the decimal point three places left; therefore, 5.0 microns = .005 mm. Measures of Length 10 millimeters (mm) = 1 centimeter (cm) 10 centimeters = 1 decimeter (dm) 10 decimeters = 1 meter (m) 1,000 meters = 1 kilometer (km) Metric and English Conversion Table Linear Measure 1 kilometer = 0.6214 mile 1 mile = 1.609 kilometers 1 meter = 39.37 inches 1 yard = 0.9144 meter 3.2808 feet 1 foot = 0.3048 meter 1.0936 yards 1 foot = 304.8 millimeters 1 centimeter = 0.3937 inch 1 inch = 2.54 centimeters 1 millimeter = 0.03937 1 inch = 25.4 millimeters 1 micron = 0.00003937 inch To convert from mm to inches; divide the millimeters by 25.4. Example: mm = 21.6535 in. Or multiply by .03937; 550 mm x .003937 = 21.6535 in. To convert from in. to mm, multiply the in. by 25.4. Example: .750 x 25.4 = 19.05 mm. Or divide by .03937: Example: .750 in. divided by .03937 = 19.05 mm.