Backflow Preventer Sizing Calculator

Get a recommended assembly type and size based on your application and peak flow rate.

Application What is being protected?

Peak design flow rate (GPM) Use max instantaneous demand, not average

Service/inlet pipe size Optional — for reference only

Enter a peak flow rate in GPM to calculate a recommended size.

Recommended Assembly

Assembly type

Rated capacity at this size

minimum recommended assembly size

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This calculator gives a general reference size based on typical published assembly flow ratings. Exact maximum flow and allowable pressure loss vary by brand and model — always confirm against the specific product's datasheet before final selection, and verify assembly type and testing requirements with your local water authority or backflow prevention program. For combined domestic + fire-line systems, or flows near a size boundary, we recommend a licensed engineer confirm final sizing.