How do you know how many words per minute you can type?

Answer 1

Depends. If you mean how many words you type per minute, you simply write a text for 5 minutes (or however long you wish), then count how many words you've written when the 5 minutes are over, and then divide it by 5.
There's several programs that can do something similar to this, though most of them work in a slightly different way.
Most of them work like this:
There's a text on your screen, and you have to type in what the text is reading, and it will then see how many (correctly spelled) words you've managed to type in said timeframe.

http://www.typeonline.co.uk/typingspeed.php is a decent example of this, though, to me, it seems a bit unproffessional.

It is important to calculate your typing accuracy as well. A good website to automatically calculate your words per minute and accuracy for free is called Typing Dude. You can visit the website at http://www.now1technologies.com/typetest . Not only does this website calculate your words per minute and accuracy it shows you the errors you made.

Answer 2

The simplest way - type a passage of text over a fixed, timed period - and divide the number of characters typed by 5. Over the whole English vocabulary - the average length of a single word is 5 characters. Therefore - say (for example) over a four minute period, you typed 1,000 characters (excluding spaces). 1000/4=250 words... 250/4 = 62.5 words per minute.

Answer 3

There are internet sites where you can test your typing speed.