Hydraulics
Pipe size calculator
Estimate the internal pipe diameter needed to carry a target flow at a chosen velocity. Use it as the inverse of the pipe flow calculator when you already know the required flow.
Outputs
- Diameter in mm
- Cross-section area
- Flow check
What pipe size do you need for 30 L/min at 1.5 m/s?
Example build-up
Target flow: 30 L/min. Average velocity: 1.5 m/s.
Estimated internal diameter is about 20.6 mm.
Formula
Area = flow / velocity
Diameter = 2 × sqrt(area / pi)
Enter the target flow and velocity
Measurement note
This is a geometric estimate. Real pipe sizing also depends on friction, pressure loss, fittings, and acceptable velocity.
What the inputs mean
Target flow
Use the expected flow you want the pipe to carry, not the supply pressure.
Velocity
Lower velocity usually means a larger pipe, but also lower friction.
Use case
Good for rough water sizing, branch selection, and quick comparison between options.