The Pipe Size Calculator estimates the minimum pipe diameter needed for a given flow rate and target velocity, and recommends the nearest standard pipe size. Simply fill in the fields above and click Calculate to get an instant result.
This calculator is part of Calculate Wiki’s Construction Calculators collection.
What You’ll Need
- Flow Rate (GPM)
- Target Velocity — typical water supply lines run 4–8 ft/s
Formula Used
Flow (cu ft/s) = Flow rate (GPM) ÷ 448.831
Required area = Flow ÷ Velocity
Diameter = √(4 × Area ÷ π)
Example Calculation
Using example inputs — Flow Rate = 20 GPM; Target Velocity = 5 ft/s — the Pipe Size Calculator returns:
| Value | Result |
|---|---|
| Minimum calculated diameter | 1.28 in |
| Recommended standard pipe size | 1.5 in |
1.5 in recommended pipe size.
Helpful Information
Results from the Pipe Size Calculator are estimates based on standard formulas used in the construction calculators field. For plumbing systems with significant pressure, safety, or code implications, consult a licensed plumber or engineer.