Accurate Project Time Estimates

Inevitably you will be asked to provide a time estimate for something you have never done before. A quick discussion on irc led to some good formulas.

Estimate how long you think it will take, double it, and then up the unit; if you don't think that applies to you, then multiple by 4 instead of 2. So if you think it's going to take 8 hours, then you get 8 hours -> 16 hours -> 16 days. Unless you think that can't possibly apply to you, because you're so good, you get 8 hours -> 32 hours -> 32 days

Mine was:

( (time you think)*2 + (time you think)/2 + (time you think)%2 )

Obviously I was being too conservative.