Everyday measurement units are often defined as fractions or multiples of other units. Fractions or multiple of SI units are named using a prefix and the name of the base unit. All prefixes are based on powers of 10. For example, a length of 1000 meters is also called a kilometer because the prefix kilo means “one thousand,” which in scientific notation is 103 (1 kilometer = 1000 m = 103 m). The prefixes used and the powers to which 10 are raised are listed in the table below.
| Prefix | Symbol | Factor | Example |
|---|---|---|---|
| femto | f | 10−15 | 1 femtosecond (fs) = 1 × 10−15 s (0.000000000000001 s) |
| pico | p | 10−12 | 1 picometer (pm) = 1 × 10−12 m (0.000000000001 m) |
| nano | n | 10−9 | 4 nanograms (ng) = 4 × 10−9 g (0.000000004 g) |
| micro | µ | 10−6 | 1 microliter (μL) = 1 × 10−6 L (0.000001 L) |
| milli | m | 10−3 | 2 millimoles (mmol) = 2 × 10−3 mol (0.002 mol) |
| centi | c | 10−2 | 7 centimeters (cm) = 7 × 10−2 m (0.07 m) |
| deci | d | 10−1 | 1 deciliter (dL) = 1 × 10−1 L (0.1 L ) |
| kilo | k | 103 | 1 kilometer (km) = 1 × 103 m (1 000 m) |
| mega | M | 106 | 3 megahertz (MHz) = 3 × 106 Hz (3 000 000 Hz) |
| giga | G | 109 | 8 gigayears (Gyr) = 8 × 109 yr (8 000 000 000 yr) |
| tera | T | 1012 | 5 terawatts (TW) = 5 × 1012 W (5 000 000 000 000 W) |
Need a refresher or more practice with scientific notation? See the sections on Math Skills for Chemistry for a review on scientific notation and exponential math.