Find the recommended pipe diameter for a desired flow rate and velocity, and see the nearest standard pipe size.
How to Use the Pipe Size Calculator
Enter the "Desired Flow Rate (L/min)" you need the pipe to carry.
Enter the "Flow Velocity (m/s)" or leave the default value of 1.5 m/s.
Click "Calculate" to see the calculated diameter and the nearest recommended standard pipe size.
Frequently Asked Questions
It uses the continuity equation Diameter = √(4 × Flow Rate ÷ (π × Velocity)), which relates flow rate, cross-sectional area, and flow velocity.
1.0–1.5 m/s is a common safe range for domestic cold water supply pipes to limit noise, erosion, and water hammer. Higher velocities (up to 2–3 m/s) may be used for short runs or larger commercial systems.
Pipes are manufactured in standard nominal sizes (15mm, 20mm, 25mm, etc.). The calculator rounds your exact calculated diameter up to the next available standard size, since you can't buy a custom diameter.
Yes, it's completely free and requires no sign-up.