Water Flow Rate Calculator
Calculate water flow rate through a pipe based on diameter, pressure, and pipe length.
Results in GPM and LPM.
Water Flow Rate
Water flow rate through a pipe is estimated using the Hazen-Williams equation (simplified for typical residential plumbing):
Q = 0.2083 × (100 / C)^1.852 × (d^4.8655) / (L^0.54) × (ΔP)^0.54
Simplified practical formula:
Q (GPM) ≈ 29.84 × C × d^2.63 × (ΔP / L)^0.54
Where:
- Q = flow rate
- C = pipe roughness coefficient (typically 130 for copper, 150 for PVC)
- d = internal pipe diameter
- ΔP = pressure differential
- L = pipe length
Unit conversions:
- GPM to LPM:
GPM × 3.78541 - LPM to GPM:
LPM × 0.26417 - Inches to mm:
inches × 25.4 - PSI to kPa:
PSI × 6.895
Common pipe sizes (internal diameter):
- 1/2 inch: Bathroom sinks, toilets
- 3/4 inch: Main supply lines, showers
- 1 inch: Larger homes, irrigation
- 1.5 inch: Commercial applications
Typical household pressure: 40–80 PSI (275–550 kPa)