Answer:
To find your average reading speed, you'll need a book with familiar words and subject. Don't time your reading speed on new words, concepts or subjects you won't get a fair result.
Set a timer for 1 minute 1 second. Here's one you can use www.online-stopwatch.com/online-countdown/
Get your book ready and start your timer. When it goes off, note what word you were on and count back to where you started reading. It's that simple.