First, figure out how much money you need to run at least two experiments*. Then tack on 3 more months of runway so you can raise another round before you run out of money. This is the minimum amount of money you should raise.
(Full Post: http://venturehacks.com/articles/seed-valuation)
Babak Nivi is a co-founder of AngelList andVenture Hacks. Previously, he was an entrepreneur-in-residence at Bessemer Venture Partners and Atlas Venture. He has worked on startups including Songbird, Grockit, and Kovio. He went to school at MIT where received 2 patents and published in Science.