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    Water Flow Rate Calculator (GPM)

    What size water pipe do I need for a given GPM?

    In Find pipe size mode, enter your target flow and the tool sizes the diameter for no more than 75% of the material velocity ceiling, then rounds up to the next standard nominal size. Friction loss at that size is computed with the Hazen-Williams equation using the material C-factor, including any equivalent length you add for fittings. It also warns if velocity still exceeds the ceiling.

    Run the numbers for your project

    Use the Water Flow Rate Calculator (GPM) to get an exact answer for your inputs.

    Open the calculator

    Related questions

    Estimates and general guidance only. Verify against your local code and AHJ before any installation. Gas, electrical, and refrigerant work is hazardous to untrained users.

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