Pipe Diameter Calculator
Find the minimum pipe inner diameter for a required flow rate at a target velocity.
How it works
- 1Enter the required volumetric flow rate and your target flow velocity.
- 2The calculator applies d = √(4Q / πv) to find the minimum internal diameter.
- 3Read the result in mm or inches, then select the next standard pipe size up.
Use cases
- Sizing water-supply pipes for residential or commercial buildings.
- Designing irrigation mains and distribution laterals.
- Selecting hydraulic lines in industrial fluid-power systems.
Frequently asked questions
What velocity should I target?
For cold-water supply, 1.5–2.5 m/s (5–8 ft/s) balances friction loss against pipe cost. Higher velocities raise noise and wear; lower risk sedimentation.
How is the formula derived?
From Q = A·v with A = π/4·d², rearranging gives d = √(4Q / πv). For Q = 0.01 m³/s at v = 2 m/s, d ≈ 0.0798 m (79.8 mm).
Why round up to a standard size?
The result is the theoretical minimum. Pipes come in fixed nominal sizes, so choosing the next size up keeps the real velocity at or below target.
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