Appendix I: SI and English Units and Conversion Factors

The most important systems of units are shown in the table below. The mks system is also known as the International System of Units (abbreviated SI), and the abbreviations sec (instead of s), gm (instead of g), and nt (instead of N) are also used. System of units Length Mass Time Force cgs system centimeter (cm) gram (g) second (s) dyne mks system meter (m) kilogram (kg) second (s) newton (nt) Engineering system foot (ft) slug second (s) pound (lb) 1 inch (in.) 2.540000 cm 1 foot (ft) 12 in. 30.480000 cm 1 yard (yd) 3 ft 91.440000 cm 1 statute mile (mi) 5280 ft 1.609344 km 1 nautical mile 6080 ft 1.853184 km 1 acre 4840 yd 2 4046.8564 m 2 1 mi 2 640 acres 2.5899881 km 2 1 fluid ounce 1/128 U.S. gallon 231/128 in. 3 29.573730 cm 3 1 U.S. gallon 4 quarts (liq) 8 pints (liq) 128 fl oz 3785.4118 cm 3

Measurement of any physical quantity involves comparison with a certain basic, arbitrarily chosen, internationally accepted reference standard called unit. The result of a measurement of a physical quantity is expressed by a number (or numerical measure) accompanied by a unit. Although the number of physical quantities appears to be very large, we need only a limited number of units for expressing all the physical quantities, since they are interrelated with one another. The units for the fundamental or base quantities are called fundamental or base units. The units of all other physical quantities can be expressed as combinations of the base units. Such units obtained for the derived quantities are called derived units. A complete set of these units, both the base units and derived units, is known as the system of units.