Pool Filter Sizing Calculator
Calculate the required filter size and flow rate for your swimming pool based on pool volume, turnover rate, and filter type.
Recommended: 6–8 hrs residential, 4–6 hrs commercial
Formulas Used
Pool Volume (gal) = Length (ft) × Width (ft) × Avg Depth (ft) × 7.48052
Required Flow Rate (GPM) = Pool Volume (gal) ÷ (Turnover Time (hrs) × 60)
Minimum Filter Area (ft²) = Flow Rate (GPM) ÷ Max Flow Rate per ft²
Recommended Filter Area (ft²) = Minimum Filter Area × 1.20 (20% safety factor)
Max Flow Rates by Filter Type: Sand = 15 GPM/ft² · Cartridge = 0.375 GPM/ft² · DE = 2 GPM/ft²
Assumptions & References
- Pool shape assumed rectangular; for irregular shapes, calculate volume separately and use a custom volume input.
- Turnover rate of 6–8 hours is standard for residential pools (APSP/ANSI 7-2013).
- Commercial pools typically require a 4–6 hour turnover per local health codes.
- Maximum filter flow rates per NSPI/APSP standards: Sand 15 GPM/ft², DE 2 GPM/ft², Cartridge 0.375 GPM/ft².
- A 20% safety factor is added to filter area to account for fouling and flow resistance over time.
- Pump HP estimate uses a rule of thumb of 1 HP per 40 GPM; actual selection must account for total dynamic head (TDH), pipe diameter, and run length.
- Backwash flow rates: Sand and DE filters require 15 GPM/ft² of filter area; cartridge filters require manual cleaning.
- 1 cubic foot = 7.48052 US gallons (exact conversion).
- References: APSP/ANSI-7, NSPI Standards, Pool & Hot Tub Alliance (PHTA) guidelines.