Filter Loading Rate Calculator

Work out filter loading rate instantly with clear inputs, formula shown and shareable results.

About Filter Loading Rate Calculator

Filtration rate is flow divided by the area of filters actually in service, expressed in cubic metres per square metre per hour, which is numerically the same as metres per hour. Rapid gravity sand filters run 5-12 m/h, and the design must check the rate when the largest filter is out for backwash.

Formulas

Filtration rate

Rate (m/h) = flow (m3/day) / (24 x effective area)

Effective area

Effective area = (filters - filters in backwash) x area per filter

Worked example

With the default values below, Filter Loading Rate Calculator returns Filtration Rate of 4.6296. Change any input above and every figure here is recalculated in your browser.

Inputs used

Filter Flowminimum 0 m3/day: 10,000 m3/day
Number Of Filtersminimum 1: 4
Area Per Filterminimum 0 m2: 30 m2
Filters Out For Backwashminimum 0: 1

Results

Filtration Rate: 4.6296
Rate With All Filters In Service: 3.4722
Effective Filter Area: 90.00
Rate In Metres Per Day: 111.111

Step by step

1Values used
2Filtration rate
3Effective area
4Filtration Rate= 4.6296
5Rate With All Filters In Service= 3.4722
6Effective Filter Area= 90.00
7Rate In Metres Per Day= 111.111

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why check the rate with a filter out?

Because the remaining filters must carry the whole flow. With four filters and one washing, the rate rises by a third, and if that pushes past the design maximum, turbidity breakthrough follows.

What limits filtration rate?

Media size and depth, floc strength and head available. Higher rates drive floc deeper into the bed, shortening runs and risking breakthrough; deeper, coarser dual media beds allow higher rates.