The table below gives indicative flow capacities for common water distribution pipe sizes at a typical design velocity of 1.5 m/s. Lower velocities reduce friction losses and water hammer; higher velocities save on pipe cost.
| Nominal size | OD (mm) | Flow @ 1.0 m/s (m³/hr) | Flow @ 1.5 m/s (m³/hr) | Flow @ 2.0 m/s (m³/hr) |
|---|---|---|---|---|
| ½” (20 mm) | 26.7 | 1.8 | 2.7 | 3.6 |
| ¾” (25 mm) | 33.4 | 2.8 | 4.2 | 5.6 |
| 1″ (32 mm) | 42.2 | 4.5 | 6.8 | 9.0 |
| 1¼” (40 mm) | 48.3 | 6.0 | 9.0 | 12.0 |
| 1½” (50 mm) | 60.3 | 9.5 | 14.3 | 19.0 |
| 2″ (63 mm) | 63.0 | 10.5 | 15.8 | 21.0 |
| 2″ (75 mm) | 75.0 | 15.0 | 22.5 | 30.0 |
| 3″ (90 mm) | 90.0 | 21.5 | 32.3 | 43.0 |
| 4″ (110 mm) | 110.0 | 32.0 | 48.0 | 64.0 |
| 6″ (160 mm) | 160.0 | 68.0 | 102.0 | 136.0 |
Note: Values are based on internal diameter for medium-class PVC/HDPE and assume clean water. Actual capacity depends on pressure class, wall thickness, fittings and total dynamic head.