SI - Metric Prefixes

Some of the physical properties measured by modern science are incredibly large, while others are infinitesimally small. While other measurement systems frequently use different units depending upon scale, the metric system uses the same basic units regardless of size.

Instead of changing units, the metric system leverages a system of prefixes to multiply or divide the standard units. Each prefix can be viewed as a type of shorthand or abbreviation that represents a specific power of ten. For physical properties that are significantly larger than a standard unit, the metric system employs the following set of prefixes:

Units Multiplied:
Prefix Abbrev. Decimal Form Exponent
deka da 10. 101
hecto h 100. 102
kilo k 1000. 103
Mega M 1,000,000. 106
Giga G 1,000,000,000. 109
Tera T 1,000,000,000,000. 1012
Peta P 1,000,000,000,000,000. 1015
Exa E 1,000,000,000,000,000,000. 1018

Each prefix can be applied to any of the standard units. Rather than representing a unique unit unto itself, a kilogram is just another way to represent a measurement of 1,000 grams. Physical properties that are significantly smaller than a standard unit, have their own set of prefixes:

Units Divided:
Prefix Abbrev. Decimal Form Exponent
deci d .1 10-1
centi c .01 10-2
milli m .001 10-3
micro µ .0000001 10-6
nano n .000000001 10-9
pico p .000000000001 10-12
femto f .000000000000001 10-15
atto a .000000000000000001 10-18

Similar to the way a kilogram represents one thousand (1,000) grams, a milligram is just shorthand for one-thousandth (.001) of a gram. Taken together, these two sets of prefixes form a complete system  allowing one to easily describe all aspects of the physical world - from the very large to the very small.

Unit Scale:
Prefix Abbrev. Decimal Form Exponent
Exa E 1,000,000,000,000,000,000. 1018
Peta P 1,000,000,000,000,000. 1015
Tera T 1,000,000,000,000. 1012
Giga G 1,000,000,000. 109
Mega M 1,000,000. 106
kilo k 1000. 103
hecto h 100. 102
deka da 10. 101
1. 100
deci d .1 10-1
centi c .01 10-2
milli m .001 10-3
micro µ .0000001 10-6
nano n .000000001 10-9
pico p .000000000001 10-12
femto f .000000000000001 10-15
atto a .000000000000000001 10-18

Notes:1) The prefixes are technically case-sensitive and there is a huge difference between a Mg. (Megagram) and mg. (milligram).

2) After kilo, the exponents increase by multiples of three, just as the exponents decrease by multiples of three after milli.