I write with a word processor called Scrivener, and I can see the word count at the bottom of the screen. (Word and Pages do this too, I think.) To write 50,000 words in a month, I have to write about 1,700 words a day, so I just aim for the word count to be 1,700 words higher than it was the day before. But when I wrote by hand and needed to know my word count, I figured out the average number of words I had on each page (usually 250-300), and then went by number of pages.