Pipe flow rate calculator
Flow rate is velocity times the inner cross-section area. Enter the actual inner diameter and the flow velocity.
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How to use it
- Enter pipe inner diameter and flow velocity.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Q = v × A with A = π d² ÷ 4. Then Q (m³/h) = Q (m³/s) × 3600, and 1 US gallon = 3.785411784 L.
Example
Inputs: Pipe inner diameter = 50 mm, Flow velocity = 2 m/s. Result: Flow rate: 14.1372 m³/h; In litres per second: 3.927 L/s; In litres per minute: 235.619 L/min.
Limits and caveats
- Assumes a full pipe and an average velocity over the section.
- Nominal pipe size differs from the inner diameter, so take the inner value from the maker table.
Questions about this tool
How do I get velocity if I know the flow?
Divide the flow in m³/s by the section area: v = Q ÷ A.
Why does doubling the diameter give 4 times the flow?
Area grows with the square of the diameter, so at the same velocity the flow is 4 times larger.
Nominal or inner diameter?
Always the inner diameter. A 2 inch nominal pipe, for example, has an inner diameter that depends on wall thickness.