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Prefixes With SI Units

Summary

Defining the various prefixes and abbreviations for SI units, including the ones you don’t need to use that much.

In another article, we list the SI base units and some of the most common derived units. Of course, there is more to the SI than just the units; prefixes are used with SI units to indicate the magnitude of the SI unit.

Each prefix has a unique symbol that is used with SI symbols (see the table below). Compound prefixes are not used, and there is never a space between a prefix symbol and the SI symbol or the prefix and the SI name (e.g., use mm and millimeter, not m m or milli meter). For prefixes and unit names that respectively end and start with a vowel, keep both vowels, except in the case of kilohm. In addition, deci-, deca-, and hecto- are not commonly used in technical writing.

Magnitude (US term)10nPrefixSymbol
septillion1024yotta-Y
sextillion1021zetta-Z
quintillion1018exa-E
quadrillion1015peta-P
trillion1012tera-T
billion109giga-G
million106mega-M
thousand103kilo-k
hundred102hecto-h
ten101deka- or deca-da
one100----
tenth10-1deci-d
hundredth10-2centi-c
thousandth10-3milli-m
millionth10-6micro-µ
billionth10-9nano-n
trillionth10-12pico-p
quadrillionth10-15femto-f
quintillionth10-18atto-a
sextillionth10-21zepto-z
septillionth10-24yocto-y

Notice that there are different prefixes that use the same letter in the lowercase or uppercase form. Take care not to mistakenly convert a given prefix abbreviation to the wrong case. For example, in the case of kilovolt, KV is frequently used when it should actually be kV. A capital K is commonly used in computing to indicate 210, so this mistake should be corrected to avoid confusion. In addition to the standard prefixes listed above, certain technical manuscripts still use the angstrom (abbreviated Å) to refer to one ten-billionth of a meter (1.0 × 10-10 m). Keep in mind, also, that µm is more commonly spelled out as micron than micrometer.

We hope that this post provides a handy resource regarding the standard SI prefixes and how to use them in your writing. Let us know if you have any questions by writing us an email. Best of luck with your writing!

Tags Writing a manuscript Editing tips SI units Measurement Abbreviations Chemistry Physics Engineering Life Sciences Field specific terminology

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