Resolution - Print Size Chart The numbers on the chart stand for dots per inch (dpi) they say the human eye does not see much beyond 96 dpi, that should give you a good example of what will work to make a good quality print.
Make Giant Art Prints of Your Favorite Photos With a Few Simple Steps
Did you know you can make large-scale art prints from most any photograph you've taken? It’s easy to make budget-friendly, giant black-and-white posters from your photographs. All you need is a high-resolution digital image of the photograph you want to enlarge. http://www.ehow.com/ehow-home/blog/make-giant-art-prints-of-your-favorite-photos-with-a-few-simple-steps/?utm_source=pinterest.com&utm_medium=referral&utm_content=blog&utm_campaign=fanpage