Hydraulics
Pipe flow guide
Pipe flow depends mainly on internal diameter and average velocity. This guide explains the basic relationships before you move to the calculator or compare common pipe sizes.
The basic flow formula
Core relationship
Flow = area × velocity
Area comes from the pipe's internal diameter, so small changes in diameter can have a large effect on flow.
Practical note
Friction, fittings, and pressure losses reduce real-world flow. Use the calculator for a quick estimate, not a final design.
Useful for quick sizing checks
Water planning
Estimate how much water a line can carry at a chosen velocity.
Pipe comparison
Compare smaller and larger diameters before choosing a branch size.
Estimator input
Use the result as a starting point for more detailed hydraulic checks.
Pipe flow examples
Pipe size calculator
Switch to the inverse calculation when you know the target flow.
Open calculator