How many horsepower for a pool pump do i need to buy for an above ground pool? pool is 18 round?

Question:i need a replacement pump, i dont know how many hp for my old pump.

Answers:
Not all same hp pumps pump the same amount of water (gpm). A Hayward, for example, would be sufficient at a 1 HP rating. The pump end design (not just the motor HP) determines the pump's flow rate as well. I have a Hayward 1HP Matrix Pump on a 21' round, and it's all the power anyone would need. (Some other brands are just as good... do you know who made the old one?)

Also, the size of your filter will limit the size pump you can use. If the filter and pump were purchased together, they were probably sized for each other. I wouldn't recommend going with a larger pump. To do so could damage the filter by exceeding its design flow rate. (Manufacturer's websites can give you all this information...)