Flow Rate Calculator
Calculate volumetric flow rate through a circular pipe from its inner diameter and flow velocity.
How it works
- 1Enter the pipe inner diameter (mm or in) and the mean flow velocity (m/s or ft/s).
- 2The calculator applies Q = (π/4)·d²·v to compute the volumetric flow rate.
- 3Results show L/s or gpm, plus m³/h or cfm and the pipe cross-section area.
Use cases
- Sizing water-supply and drain pipes in building plumbing design.
- Verifying pump selection by matching rated flow to pipe capacity.
- Estimating irrigation or process flow through existing pipework.
Frequently asked questions
What formula does the calculator use?
Q = A × v = (π/4)·d²·v. A 100 mm pipe at 2 m/s gives A = 0.007854 m² and Q ≈ 0.01571 m³/s (15.71 L/s).
What is a good flow velocity for water pipes?
Keep velocity between 1 and 3 m/s. Below 0.5 m/s sediment can settle; above 3 m/s noise, erosion, and surges become a problem.
How do I convert L/s, m³/h, and gpm?
1 L/s = 3.6 m³/h ≈ 15.85 gpm. Toggle between metric and imperial to see the result in your preferred units.
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