Up to the S.I. contents page.

# What Are The Prefixes?

The following two tables show the most commonly used prefixes for S.I. base units.

Firstly, we have prefixes that talk about multiples of a unit (i.e. more than one)...

Multiple Prefix Abbreviation
10 deca da
10^2 = 100 hecto h
10^3 = 1000 kilo k
10^6 mega M
10^9 giga G
10^12 tera T

... and now we have the prefixes corresponding to fractions of a whole unit ...

Fraction Prefix Abbreviation
10^-1 = 1/10 deci d
10^-2 = 1/100 centi c
10^-3 = 1/1000 milli m
10^-6 micro µ
10^-9 nano n
10^-12 pico p
10^-15 femto f
10^-18 atto a

### NOTES:

1. A notation like 10^6 means 10 raised to power 6, or a "1" followed by six "0"s (i.e. 10^6=1000000). We represent it this way because unfortunately superscripts are not possible in this program.

2. It is important not just to get an abbreviation's letter(s) correct, but also to have it in the proper case (upper- or lower-case). There is a big difference between 1 mm and 1 Mm!

3. The abbreviation for the prefix "micro" (µ ) is the Greek letter mu.

4. Finally, notice how, except for the first couple of entries in each table, the prefixes increase (or decrease) by multiples of 1000. Historically, it has been found that this keeps measurements to a managable number of digits. For example, it is easy to tell the size of 475.1 grams. However, to the nearest 1000, how big is 12650384? Notice how you had to count the digits carefully? It could have been easier if I wrote this number as 12650.384 x 10^3. Then you can quickly see that it is closest to 12 650 lots of one thousand.

On to Standards