How to format numbers and thousands with decimals in Excel?

To display 23567 as 23.6K, you can use this custom number format:

##0.0,"K"

Or as pointed out in the comments, depending on your regional settings for the usage of , and . use the following format:

#0,0."K"

You could also display it as 23.57K with:

##0.00, "K"

Note the place of the comma. By adding a second comma you can also interpret millions, so 1234567 would be displayed as 1.2m:

##0.0,, "m"

The comma works as the thousands separator, and since all the examples have nothing to the right, i.e. no 0 or #, then nothing more is displayed other than the string.

Another very cool example is this:

[<1000000]£##0, "k";[>=1000000]£0.0,," m"

It will show any number in the millions as £1.2 m, and anything less than a million as £800 k

Custom numbers can also be used in charts.