It is specific to your life situation. You could try calculating a base expenses rate with the Federal Poverty Level. That should cover a basic roof over your head, simple food, thrift store clothes, insurance and healthcare and transportation. I know in my family, we've always spent just around the poverty level and that's including all the extras like gifts and travel. We don't suffer at all at that level because we enjoy being debt free(except an affordable mortgage)and are in good health living a non-consumerist lifestyle.
My household of 5, with an income that has never exceed $40K(but will finally this year),has never spent more than $30K a year. This has allowed us to save anywhere from 20-45% of gross income. Right now we're facing the challenge of moving in to a new house that is 3X the size of our last home. The taxes and utilities are much cheaper here in CO than in NJ which will help even things out. But now we live 1750 miles away from our families, greatly increasing our vacation/travel expenses. On paper our expenses should come out to be $32-36K in 2013. We spent just $28.5K last year. I'm going to rethink as much as I can and aim for spending just $30K. I'm excited to learn new ways to save. One I know for sure will be partially heating with wood instead of electric. The new property has tons of dead wood to clear and a fireplace.
I think keeping your mind open to learning and your options open for trying new things will overall be better than focusing on a specific number. You may be surprised one year, as I was, to discover you saved 40% of your gross income. :D