Filter Loading Rate Calculator
How hard are your filters working right now? Enter plant flow and filter area to get the filtration rate in gpm/ft² — the number that decides whether you’re inside your design basis.
Filtration Rate
| Item | Value |
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How the calculation works
Formulas
Filtration rate (gpm/ft²) = flow (gpm) ÷ total filter area (ft²)
Total filter area = filters in service × area per filter
1 MGD = 694.44 gpm · 1 gpm/ft² = 2.4447 m/h
Filtration rate (gpm/ft²) = flow (gpm) ÷ total filter area (ft²)
Total filter area = filters in service × area per filter
1 MGD = 694.44 gpm · 1 gpm/ft² = 2.4447 m/h
Notes & limitations
The conventional rapid-sand design range of 2–6 gpm/ft² is from the Ten State Standards (Great Lakes) and AWWA filtration guidance. Your state may set a lower ceiling — the permit governs.
- Use filters actually in service. The rate jumps when one filter is in backwash — check the worst case with one unit out.
- Rate alone doesn’t set performance: media condition, coagulation quality, and backwash effectiveness matter as much. Track effluent turbidity against the 0.3 NTU / 95% rule (40 CFR 141.73).
- High-rate and deep-bed designs run above 6 gpm/ft² by design; this warning applies to conventional rapid sand.
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