Filtration Rate Calculator

Calculate filter area, media volume, and backwash requirements from flow rate and loading rate.

Inputs

Plant Flow Rate

MGD

Filter Type

Filtration Loading Rate

gpm/ft²

Media Depth

inches

Filter Run Length

hours

Tab to move between fields

Results

Total Filter Area Required

868 sq ft

≈ 7 parking spaces

Number of Filters

Area per Filter289 sq ft

Filter TypeDual Media (anthracite/sand)

Filtration Velocity9.8 m/h

Empty Bed Contact Time4.7 min

Media Volume80 cubic yards

Clean Bed Headloss1.3 ft

Terminal Headloss3.8 ft

Backwash Water Use1.6% of production

Media Replacement Cost$54,253.00

Run Volume (gal)10,000,000

How to Use This Calculator

Enter Plant Flow Rate (MGD) — the design flow the filter bank must handle including peak demand.
Select Filter Type (rapid sand, dual media, greensand, slow sand) to apply the appropriate loading rate range.
Enter Filtration Loading Rate (gpm/ft²) from design standards or regulatory limits for your filter type.
Input Media Depth (inches) and Filter Run Length (hours) from your operational data or design basis.
Review Total Filter Area Required (sq ft) and Number of Filters to plan filter cell sizing and redundancy.
Check Area per Filter to verify each cell falls within the practical construction size range for your design.

How the result changes with Filtration Loading Rate

Filtration Loading Rate	Total Filter Area Required	Number of Filters
1.95	1,781 sq ft	5
5.57	623 sq ft	2
9.93	350 sq ft	2
14	248 sq ft	2

What each input means

Plant Flow Rate: Design flow rate in million gallons per day.
Filter Type: 1 = Rapid Sand, 2 = Dual Media, 3 = GAC, 4 = Membrane.
Filtration Loading Rate: Flow per unit filter area. Typical: 2-6 gpm/ft² for gravity filters, 10-15 for membranes.
Media Depth: Total filter media depth. Sand: 24-30", dual media: 24-36", GAC: 36-60".
Filter Run Length: Average filter run time between backwashes. Typical: 24-72 hours.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Plant Flow Rate = 5, Filter Type = 2, Filtration Loading Rate = 4, Media Depth = 30 = 5 input(s) provided
Calculate Total Filter Area Required
Total Filter Area Required
868 = 868
Calculate Number of Filters
Number of Filters
3 = 3
Calculate Area per Filter
Area per Filter
289 = 289
Calculate Filter Type
Filter Type
Dual Media (anthracite/sand) = Dual Media (anthracite/sand)

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