Here's Pentair's page for one of their cartridge filters:
http://www.pentairpool.com/pool-owne...filters-28.htm

Click on the "specs" tab, to match a filter to your pool volume and water flow. It looks like the smallest one would be within specs on your pool. But, with cartridge filters, there's no downside that I know of to oversizing them, and you'll be able to go longer between cleaning with an oversized filter.