Size water supply pipes based on flow rate and velocity limits.
| Cold Water Supply | 1.5 - 2.5 m/s |
| Hot Water Supply | 1.0 - 2.0 m/s |
| Main Distribution | 2.0 - 3.0 m/s |
Enter flow rate and click Calculate
Water supply pipe sizing balances adequate flow delivery with acceptable pressure drop and velocity. The goal is to select the smallest economical pipe that meets flow requirements while keeping velocity within acceptable limits to prevent noise, erosion, and water hammer.
Q = A × V → D = √(4Q / πV)
Where: Q = flow rate, A = pipe area, V = velocity, D = diameter
| Application | Velocity (m/s) | Velocity (fps) |
|---|---|---|
| Cold Water Supply (Residential) | 1.0 - 2.0 | 3 - 6 |
| Cold Water Supply (Commercial) | 1.5 - 3.0 | 5 - 10 |
| Hot Water Circulation | 0.5 - 1.0 | 2 - 3 |
| Fire Protection Mains | Up to 6.0 | Up to 20 |
| Pump Suction | 0.5 - 1.5 | 2 - 5 |
| Pump Discharge | 1.5 - 3.0 | 5 - 10 |
Too Low (< 0.5 m/s): Sediment accumulation, stagnation, bacterial growth risk, wasted pipe material cost.
Too High (> 3 m/s): Excessive noise, erosion of pipe walls, water hammer risk, high pressure drops, shortened valve/fitting life.
Pipes are manufactured in standard nominal sizes. After calculating the theoretical diameter, select the next larger standard size:
Common DN Sizes: 15, 20, 25, 32, 40, 50, 65, 80, 100, 125, 150, 200, 250, 300 mm
Common NPS Sizes: 1/2", 3/4", 1", 1-1/4", 1-1/2", 2", 2-1/2", 3", 4", 5", 6", 8", 10", 12"
Future Expansion: Consider upsizing main distribution pipes for future load growth.
Pressure Constraints: Higher velocities mean more pressure drop. Ensure adequate residual pressure at fixtures (typically 15-20 psi minimum).
Material Selection: Copper, PEX, CPVC, and stainless steel have different flow characteristics and pressure ratings.