Definition
A set of standard word-parts attached to the front of a metric unit to multiply or divide it by a power of ten. Each prefix has a fixed symbol and a fixed numerical value, so the same prefix carries the same meaning regardless of which base unit it is attached to (meter, gram, liter, hertz, watt, volt, ampere, etc.). Common prefixes include kilo- (1,000), hecto- (100), deca- (10), deci- (0.1), centi- (0.01), milli- (0.001), micro- (0.000001), mega- (1,000,000), and giga- (1,000,000,000).
Plain English
Small word-pieces like kilo, milli, or mega that you stick on the front of a metric unit to make it bigger or smaller by a set amount. For example, kilo means a thousand, so a kilogram is a thousand grams and a kilohertz is a thousand hertz.
Context Anchor
Pilots may see metric prefixes in aircraft manuals, maintenance measurements, weather information, charts, and international aviation documents.
Derivation
The prefixes come from Greek and Latin number words. Kilo- is from Greek for 'thousand,' milli- is from Latin for 'thousandth,' mega- is Greek for 'great' or 'large,' and micro- is Greek for 'small.' Knowing the root word hints at the size: 'mega' sounds big, 'micro' sounds small.
Why Pilots Care
Misreading a prefix changes the value by a factor of a thousand or more. A radio set to the wrong band, a current rating misread as milliamps instead of amps, or a frequency mistaken between kHz and MHz can cause real operational problems.
Intuition Check
Do not treat a metric prefix as a separate unit. The prefix only changes the size of the unit it is attached to.
Example Sentence 1
VHF communication frequencies are expressed in megahertz, while ADF frequencies are expressed in kilohertz.
Example Sentence 2
When converting fuel quantity on an international flight plan, the pilot applied metric prefixes to switch between liters and kilograms.