Pipe Sizing Calculator
Estimate a pipe diameter from entered flow and pressure assumptions, then review the calculated velocity and pressure-loss outputs.
How the estimate works
Flow velocity = volumetric flow ÷ internal pipe area; area = π × internal diameter² ÷ 4.
Metric worked example
Inputs: 1 L/s through 25 mm internal diameter
Working: Area = π × 0.025² ÷ 4 ≈ 0.000491 m²; velocity ≈ 1 ÷ 1,000 ÷ 0.000491 = 2.04 m/s
Result: About 2.04 m/s velocity
US customary worked example
Inputs: 15.85 US gpm through 0.984 in internal diameter
Working: Flow ≈ 0.0353 ft³/s; area = π × (0.984 ÷ 24)² ≈ 0.00527 ft²; velocity ≈ 6.7 ft/s
Result: About 6.7 ft/s velocity
Units and regional checks
Use actual internal diameter, material, flow and pressure conditions. Plumbing sizing requirements and accepted limits depend on system and jurisdiction.
Frequently asked questions
Does nominal pipe size equal internal diameter?
No. Nominal size is a product designation; internal diameter varies with material and wall thickness.
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