Pipe Sizing Calculator

Recommend a pipe diameter for a given flow rate, keeping velocity within safe limits for the material.

1/2 in3/4 in1 in
PIPE SIZE
—
recommended

Usage Tip

Mains are usually 3/4 in to 1 in; single-fixture branches are often 1/2 in.

THE MATH
d = √(0.408 × GPM ÷ vmax)
Where: GPM = design flow  •  v max = safe velocity for the material
• Round up to a standard pipe size
• Undersizing causes noise and pressure loss
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The calculators and tools on Formula Factory are provided for general guidance and informational purposes only. Results are estimates based on standard formulas and the values you enter — they do not constitute professional engineering, electrical, or architectural advice. Always verify calculations with a qualified professional before making decisions for any safety-critical, code-compliance, or commercial application. Formula Factory makes no representations or warranties as to the accuracy or completeness of any result, and accepts no liability for errors, omissions, or any outcomes arising from reliance on this information.