A standard 4" inside diameter pipe carries 195.85 GPM (741.38 Liters/min) at standard design velocity (5 ft/s) and up to 313.37 GPM at maximum allowable cold water velocity (8 ft/s). Part of our master Pipe Flow Rate Calculator and Copper Flow Rate suite.
Flow results depend on internal pipe diameter and velocity. For actual installations, consider system head loss and friction fittings.
Volumetric water flow in US Gallons per Minute (GPM), Liters per Minute, and Liters per Second across fluid velocities (1 to 12 ft/s).
| Velocity (ft/s) | Flow Rate (GPM) | Liters / Min (L/min) | Liters / Sec (L/s) | Cubic Ft / Sec (cfs) | Hydraulic Status |
|---|---|---|---|---|---|
| 1 ft/s | 39.17 GPM | 148.3 L/min | 2.472 L/s | 0.0873 cfs | ✓ Quiet / Hot Water Safe |
| 2 ft/s | 78.34 GPM | 296.5 L/min | 4.942 L/s | 0.1745 cfs | ✓ Quiet / Hot Water Safe |
| 3 ft/s | 117.50 GPM | 444.8 L/min | 7.413 L/s | 0.2618 cfs | ✓ Quiet / Hot Water Safe |
| 4 ft/s | 156.67 GPM | 593.1 L/min | 9.885 L/s | 0.3491 cfs | ✓ Quiet / Hot Water Safe |
| 5 ft/s | 195.84 GPM | 741.3 L/min | 12.355 L/s | 0.4363 cfs | ✓ Design Standard (5 ft/s) |
| 6 ft/s | 235.01 GPM | 889.6 L/min | 14.827 L/s | 0.5236 cfs | ⚠ Cold Water Max (8 ft/s) |
| 7 ft/s | 274.18 GPM | 1037.9 L/min | 17.298 L/s | 0.6109 cfs | ⚠ Cold Water Max (8 ft/s) |
| 8 ft/s | 313.34 GPM | 1186.1 L/min | 19.768 L/s | 0.6981 cfs | ⚠ Cold Water Max (8 ft/s) |
| 10 ft/s | 391.68 GPM | 1482.7 L/min | 24.712 L/s | 0.8727 cfs | ⛔ High Velocity / Erosive |
| 12 ft/s | 470.02 GPM | 1779.2 L/min | 29.653 L/s | 1.0472 cfs | ⛔ High Velocity / Erosive |
Volumetric continuity equation $Q = A \times v$ applied to circular pipes.
Compute circular cross-sectional area in square inches:
A = \pi \times (2)^2 = 12.5664 sq in Divide square inches by 144:
A_sqft = 12.5664 / 144 = 0.08727 sq ft Multiply area by design velocity (v = 5 ft/s):
Q_cfs = 0.08727 \times 5 = 0.4363 cfs Multiply cubic feet per second by 448.831 (GPM conversion factor):
Q_gpm = 0.4363 \times 448.83 = 195.85 GPM Noise thresholds, maximum fixture capacities, and erosion limits.
Trade Hydraulic Advisory: Primary municipal distribution lines and heavy commercial central utility feeds.
Explore volumetric GPM capacities across other plumbing supply and main line diameters.
Engineering questions and velocity guidelines for 4" piping.
At 5 ft/s velocity, a 4-inch pipe delivers 195.85 GPM (741.38 L/min). At 8 ft/s, it carries 313.37 GPM (1,186.20 L/min).