--- title: "Cartridge Filter Sizing Calculator: How Many Cartridges for Your Flow | Filtsap" description: "How many filter cartridges and what housing size do you need? Enter flow and micron rating to get the number of 10, 20, 30 or 40 inch cartridges and the housing configuration." source: https://www.filtsap.com/tools/cartridge-filter-sizing-calculator/ updated: 2026-10-23 --- Free calculator # Cartridge filter sizing calculator Enter your flow and micron rating. The calculator tells you how many 10-inch-equivalent cartridges you need, then turns that into a housing: for example a 5-round 40-inch SS housing, or a set of 20-inch jumbo housings. ## Result Results appear here as you type. ## 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](https://www.filtsap.com/products/pp-spun-filter-cartridge/) , [SS cartridge filter housings](https://www.filtsap.com/products/ss-filter-housing/) , [micron rating guide](https://www.filtsap.com/guides/filter-micron-rating-guide/) , [when to replace cartridges](https://www.filtsap.com/guides/when-to-replace-filter-cartridge/) . ## 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. More calculators - [RO plant calculator](https://www.filtsap.com/tools/ro-plant-calculator/) - [Water softener sizing calculator](https://www.filtsap.com/tools/water-softener-calculator/) - [Pressure sand and carbon filter sizing](https://www.filtsap.com/tools/pressure-filter-sizing-calculator/) - [SDI calculator](https://www.filtsap.com/tools/sdi-calculator/) - [Water treatment unit converter](https://www.filtsap.com/tools/water-unit-converter/) ## Need an exact design? Send your water analysis and flow. An engineer checks it and replies on WhatsApp. [Request a quote](https://www.filtsap.com/get-quote/) ## Need filters, spares or a new plant? Send the details on WhatsApp or through the form. An engineer reads every enquiry before we quote. [Get a quote](https://www.filtsap.com/get-quote/) [WhatsApp](https://wa.me/918160852169?text=Hello%20Filtsap%2C%20I%20need%20a%20quote.)