SI Prefixes

ValueSI NameSI Symbol
10 1dekada
10 2hectoh
10 3kilok
10 6megaM
10 9gigaG
10 12teraT
10 15petaP
10 18exaE
10 21zettaZ
10 24yottaY
10 -1decid
10 -2centic
10 -3millim
10 -6microยต
10 -9nanon
10 -12picop
10 -15femtof
10 -18attoa
10 -21zeptoz
10 -24yoctoy

Here is my chart listing the prefix names and their values. This might be useful for students who are studying GCSE and need to know how to write them. Their meanings are very simple to determine as each has a value.

For example, giga represents ten to the power of nine, which means 1 followed by nine zeros.

The table shows all the values from the smallest to the largest. The smallest value yocto is 1/1000 000 000 000 000 000 000 000.

The largest value yotta is 1000 000 000 000 000 000 000 000.

Capitalisation Rules for Prefix Symbols

As you can see from the table, all the names are in lower case. Even mega, giga, tera are written out in lower case. Majority of the symbols are also in lower case except for those ranging from mega to yotta.

A common mistake students make is when writing the symbol for kilo. They use a capital letter. In fact, many of my teachers used to make that mistake as well, however the symbol and name for kilo are in lower case.

The capital letter K represents Kelvin. In the field of Information Technology Ki represents the value 1024.

All symbols are in the Times Roman font. They must be upright and not italics. Even if your document uses another font, the symbols must be Times Roman.

Grouping Prefix and SI Units

A group consists of a number you wish to express, followed by a space, followed by the prefix, followed by the unit. This is the proper order in which to group and write these symbols.

Writing Large Numbers

Never separate zeros with commas, instead use a fine space to group the zeros. Groups of three zeros are preferred.

Many people use commas instead of spaces, which is not acceptable today.

For example, giga represents 1 followed by nine zeros. Therefore it is written as 1 000 000 000 or it can be written as 1000 000 000. Using spaces to group the zeros is acceptable.

Similarly micro is represented by 1/1000 000. Using spaces makes it easier for humans to read numbers quickly without making errors.


Teachers Tips

A good educator should spend the first lesson showing students how to write the units and symbols properly, and then use that format continuously throughout the course.

Back in my day when I was studying Advanced Level Physics the teacher hated the SI Units. He covered it very briefly as a topic simply because it was in the syllabus, and then he went back to his own style of writing the units for the rest of the course.

Not only did he hate SI he also hated the metric system. Consequently, all of his example questions were in inches, feet, pounds... Not surprisingly, only one person ever passed his class in any given year. That is poor quality education. It took me many years to un-learn the bad habits he had taught me.