Syntax
Tutorial with example
In this tutorial we go through all the count functions. Below you can see the keynotes of the tutorial, so you can jump ahead to the one you need:
02:44 COUNT text (#ERROR), 03:24 COUNT numbers, 04:20 COUNT blanks, 04:56 COUNT dates
05:36 COUNTA text, 06:44 COUNTA numbers
07:27 COUNTX
09:16 COUNTAX
09:58 DISTINCTCOUNT
10:59 COUNTROWS(DISTINCT)
12:06 COUNTBLANK
12:34 COUNTROWS, 13:32 COUNTROWS with columns (#ERROR), 14:33 COUNTROWS with an expressionsion

Download example file:
Download the sample file here.
Remarks
If you do not need to count cells that contain logical values or text (in other words, if you want to count only cells that contain numbers), use the COUNT or COUNTX functions.
When the function does not find any rows to count, the function returns a blank. When there are rows, but none of them meet the specified criteria, then the function returns 0.
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/Ruth