Pipe Diameter for Flow
D = 2 × √(GPM / (velocity × π × 144 × 7.481 / 60)). Find pipe size to deliver target GPM.
Result
Recommended pipe
1"
Theoretical 0.904", round up to standard.
- Target flow10 GPM
- Velocity limit5 ft/s
- Flow (ft³/s)0.02228
- Required area (in²)0.6417
- Theoretical diameter0.904"
- Recommended size1"
Step-by-step
- Convert GPM to cubic ft/s: 10 × 0.002228 = 0.02228 cfs.
- Area = flow / velocity = 0.02228 / 5 = 0.004456 ft² = 0.6417 in².
- D = 2√(A/π) = 0.904". Round up: 1".
How to use this calculator
- Enter target flow GPM.
- Set max velocity (5-8 ft/s residential).
- Read pipe size.
About this calculator
Pipe sizing balances flow rate against velocity (noise + erosion). Common limits: domestic 5-8 ft/s, commercial 8-10, industrial 10-12. Faster = smaller pipe but more wear, noise, and pressure drop. ½" pipe handles ~3 GPM at 5 ft/s; ¾" handles ~7 GPM; 1" handles ~12 GPM. Standard residential: ¾" mains, ½" branches. Verify with manufacturer flow charts for fixture types.
Frequently asked
Noise above 8 ft/s is audible. Above 10 ft/s erodes pipe walls (especially copper). Hammer-noise risk.
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