The other day on a forum I frequent, a new writer asked how many articles she had to write a day to make a living as a freelance writer. Most of us seasoned vets answered, "It depends."
First, you have to decide how much money you need to make a day to live comfortably.

I have decided that I need to make around $75 a day to meet my financial needs. How many articles I do depends on my client. I have one client that pays $100 per article. One article and I'm good for the day's goal. If I'm writing for Demand Studios I need to write around 4 $20 articles or around 5 $15 articles to meet my goal. I rarely just write for DS in a day, though. I have another project that pays around $35 per article, so I'll combine one $35 article with 2 DS articles and call it a day. On days I particularly love, I'll have a client that pays $200 and up for an article. After those days, well, I can take a few days off, can't I?