How to measure
- Length: measure from the outer edge of one end cap to the other (not just the fabric).
- Outside diameter (OD): measure across the widest part of the end cap.
- Top opening: open hole (and its inside diameter), closed, or molded handle.
- Bottom opening: same as above. Many spa cartridges have different threads or handles.
Write these down along with any numbers printed on the end cap.
Common sizes
| Filter | Typical cartridge OD × length |
|---|---|
| Hayward Star-Clear C-500 | 7" × 19-5/8" |
| Hayward Star-Clear Plus C-900 | 8-15/16" × 17-3/8" |
| Hayward Star-Clear Plus C-1200 | 8-15/16" × 23-3/8" |
| Hayward Star-Clear Plus C-1750 | 8-15/16" × 28-3/16" |
| Rainbow Dynamic 50 (spa) | 5" × 13" |
See every model in the filter finder: you can search by dimensions.
Square footage
The sq ft rating is the total fabric area. More area means lower pressure and longer intervals between cleanings. Some aftermarket “upgrades” fit the same housing with more pleats: check the dimensions match.
