Metric Prefixes

NOTE

It is assumed here that the reader has a basic understanding of the metric system. If you are unfamiliar with the metric system, please refer to the Standards for Distance document.

Measuring very large or very small quantities with just a single unit can be difficult. For example, the distance from the Earth to the Moon is about 384,400,000 meters, which is a very large number. To make it easier to work with these kinds of distances, we use metric prefixes.

Metric prefixes are short words that we put in front of the unit's word to change its size. For example, a "kilo"meter is equal to 1,000 meters, and a "milli"meter is equal to 0.001 meters. There are many different metric prefixes, each with its own meaning.

• Yotta- (Y): 1,000,000,000,000,000,000,000,000 times the base unit
• Zetta- (Z): 1,000,000,000,000,000,000,000 times the base unit
• Exa- (E): 1,000,000,000,000,000,000 times the base unit
• Peta- (P): 1,000,000,000,000,000 times the base unit
• Tera- (T): 1,000,000,000,000 times the base unit
• Giga- (G): 1,000,000,000 times the base unit
• Mega- (M): 1,000,000 times the base unit
• Kilo- (k): 1,000 times the base unit
• Hecto- (h): 100 times the base unit
• Deca- (da): 10 times the base unit
• Deci- (d): 0.1 times the base unit
• Centi- (c): 0.01 times the base unit
• Milli- (m): 0.001 times the base unit
• Micro- (µ): 0.000001 times the base unit
• Nano- (n): 0.000000001 times the base unit
• Pico- (p): 0.000000000001 times the base unit
• Femto- (f): 0.000000000000001 times the base unit
• Atto- (a): 0.000000000000000001 times the base unit
• Zepto- (z): 0.000000000000000000001 times the base unit
• Yocto- (y): 0.000000000000000000000001 times the base unit

Some example sizes:

• The distance from the Earth to the Moon is about 384,400 kilometers.
• A single red blood cell is about 7 micrometers wide.
• The width of a human hair is about 0.1 millimeters.
• An adult human is about 1.7 meters tall.
• A single atom is about 80 picometers wide.

Converting Between Units

Converting between different units of distance is very easy with the metric system. All you need to do is multiply or divide by the appropriate factor. For example, to convert 5 kilometers to meters, you would multiply by 1,000:

$$5\text{ km}\times 1,000=5,000\text{ m}$$

To convert 10 millimeters to centimeters, you would divide by 10:

$$10\text{ mm}÷10=1\text{ cm}$$

Other uses of prefixes

Metric prefixes are not just used for distance. They can also be used for other units of measurement, such as mass, volume, and time. For example, a "kilo"gram is equal to 1,000 grams, and a "milli"liter is equal to 0.001 liters.

More information about the other kinda of measurements can be found in the Standards for Mass and Standards for Volume documents.