5 UNITS OF MEASUREMENT THE INTERNATIONAL SYSTEM OF UNITS The International System of Units, or SI (from the French Système international d unités), is the modern revision of the metric system. It is the world s most widely used system of measurement, both in everyday commerce and in science. Using the same standards of measurement makes it easier for scientists to communicate with one another. The SI is an evolving system; it can be modified through international agreement as the technology and precision of measurement progresses and improves. The SI consists of seven fundamental units: kilogram, meter, candela, second, ampere, kelvin, and mole each representing different kinds of physical quantities with a number of other derived units. The SI allows easy multiplication when switching among units having the same base but different prefixes to form decimal multiples or submultiples, that is smaller or larger quantities. SI Base Units PHYSICAL QUANTITY QUANTITY SYMBOL BASIC SI UNIT NAME UNIT SYMBOL length l, b, d, h, r, s, etc. metre m mass m kilogram kg time t second s electric current I ampere A thermodynamic temperature T kelvin K amount of substance n mole mol luminous intensity Iv candela cd SI Prefixes PREFIX SYMBOL LONG/SHORT SCALE (10N) FACTOR OF BASE UNIT giga- G Milliard / Billion 109 1 000 000 000 mega- M Million 106 1 000 000 kilo- k Thousand 103 1 000 2 hecto- h Hundred 10 deka- da Ten 101 10 deci- d Tenth 10 1 0.1 2 100 0.01 centi- c Hundredth 10 milli- m Thousandth 10 3 0.001 micro- m Millionth 10 6 0.000 001 9 nano- n Milliardth / Billionth 10 pico- p Billionth / Trillionth 10 12 0.000 000 001 0.000 000 000 001 5 UNITS OF MEASUREMENT 273