How the calculator works
Each micron rating has a safe flow per 10-inch length of cartridge. Running above it shortens cartridge life and lets dirt through. The calculator uses conservative values for spun polypropylene cartridges:
| Micron | Design flow per 10" length |
|---|---|
| 1 µm | 0.45 m³/hr |
| 5 µm | 0.7 m³/hr |
| 10 µm | 0.9 m³/hr |
| 25 µm | 1.1 m³/hr |
- 10-inch equivalents = flow ÷ design flow, rounded up.
- Cartridges = equivalents ÷ (length ÷ 10), rounded up to the next standard housing (1, 3, 5, 7, 9, 12, 15, 19, 25 or 30 rounds).
Pleated cartridges have several times the surface area of spun ones and can take more flow per length. For flows above about 40 m³/hr, a high-flow cartridge housing is usually smaller and cheaper to run.
Related: PP spun cartridges, SS cartridge filter housings, micron rating guide, when to replace cartridges.
FAQs
How many 40 inch cartridges do I need for 10 m³/hr?
At 5 micron, about 15 ten-inch equivalents, which is four 40-inch cartridges. A standard 5-round 40-inch housing gives some margin.
Can I use one big cartridge instead of several small ones?
Yes, if it has the same filter area. A 20-inch jumbo (4.5-inch diameter) cartridge holds several times the dirt of a standard 2.5-inch one.
What micron cartridge should go before an RO?
5 micron is standard. Use 1 micron if the feed water has fine silt or your SDI is high.