The .25lb/pp/day seems a bit heavy but as folks say - you don't want to run out of propane. A lot of this depends on how you use your fuel, but with this calculation I would imagine you would NEVER run out of propane. If you are looking to estimate closer, you need to take a bunch of factors into consideration:
- Do you always have a hot breakfast?
- Are you heating some or all of your dish water?
- Making pasta or other meals that require longer cook times?
- Using fuel for non-cooking uses (tiki, fire pit, etc?)
Of course, at a certain point, you need to decide how much brain damage you want to go through before just using a gross calculation like above.
Another point I would make is that I typically opt for multiple sources for propane. If my calc says 20lbs, I would bring a couple of 11's or a 20 and a small 5 just in case something happens with one tank.