A question we get asked a lot is "How big a pump do I need for my pool?" The answer is as diverse as the pools out there but, let me make a few points to start you in the right direction. First, to get the best filtration you want the water moving as slow as possible. If you get a small filter and a big pump you going to litteraly push debris through the filtration media (sand, DE or cartridge). What this means is to use bigger plumbing so you can move the same amount of water at a slower speed and get the right, or even over sized, filter.
Now people always think they have a big pool so they need a big pump. This is rarely the case. When my father in law put his pool in he wanted to go big. Living in a rural area and knowing someone in the business he was able to put in a 26 X 40 pool that holds 48,000 gallons of water. This is double the water in an average backyard pool. His filtration runs on a 3/4 HP energy efficient pump. The plumbing is all two inch and it's running through a 30" Sand Filter. The water is crystal clear even with a very high bather load!
The right plumbing and the right filter make the difference. As a home owner to find out what size is best for you contact your local pool dealer and if your a dealer ask your distributor or local manufacturers rep for advice.
Bigger isn't always better and remember that a 1/2 HP pump uses half the electricity of a 1 HP pump so its green too!