💧 Sand Filter Calculator
Enter a design flow rate and filtration rate to size a rapid sand filter — the required bed area, the minimum tank diameter, and the backwash flow your pump must supply.
💧 Size Your Sand Filter
What is a Sand Filter Calculator?
A sand filter calculator sizes a rapid (high-rate) sand filter from two inputs: the design flow rate and the filtration rate the media runs at. Dividing flow by rate gives the required bed area, from which the tool derives the minimum tank diameter and the backwash flow needed to clean the bed.
Enter the flow in gallons per minute and, if different from the 15 gpm/ft² default, your filtration and backwash rates. These are estimates for planning; media type, grain size, water quality, and the filter's rated range all affect real performance, so confirm against the manufacturer's data.
❓ Frequently Asked Questions
How do I size a rapid sand filter?
Divide the design flow rate by the filtration rate to get the required bed area. At 60 gpm with a high-rate filtration rate of 15 gpm per square foot, the area is 60 ÷ 15 = 4 square feet, which needs a tank about 2.26 feet (27 inches) in diameter. The calculator also returns the backwash flow.
What filtration rate should I use?
High-rate sand filters typically run at about 15 gpm per square foot, which is the default here. Slow sand filters run far lower (well under 1 gpm/ft²) and need much larger beds. Use the rate specified for your filter media and application; a lower rate means a bigger bed but finer filtration.
Why does the calculator report a backwash flow?
A sand filter has to be periodically reversed — backwashed — to lift and rinse trapped dirt out of the bed. The backwash flow is the bed area times the backwash rate (about 15 gpm/ft²). Your pump and plumbing must be able to supply that flow, or the bed will not clean properly and will clog over time.
Are these sand filter figures exact?
They are planning estimates. Real sizing depends on media type and grain size, water quality, temperature, and the specific filter's rated range. Use these numbers to scope a design or check a spec, then confirm against the manufacturer's data and local code before building or buying.