Water Flow Calculator
Estimate GPM flow rate through your pipes
Nominal pipe size
Static pressure
Total length of pipe run
Affects friction coefficient
Flow Rate
—
GPM
Water Velocity
—
ft/s
Pressure Loss
—
psi
Disclaimer: Results are estimates based on standard formulas. Not a substitute for professional advice from a licensed contractor, engineer, or architect. Verify all calculations before making purchasing or construction decisions.
How to Use This Calculator
Our calculator uses the Hazen-Williams formula to estimate GPM flow rates through pipes.
- Identify pipe diameter and material
- Measure available water pressure
- Determine total pipe run length
- Enter specifications
Expert Insights
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Calculation Formula
Flow Rate: Q = 0.442 x C x D^2.63 x (P/L)^0.54
Pressure Loss (psi) = 4.52 x Q^1.85 / (C^1.85 x D^4.87) x L
Where C = roughness, D = diameter (in), P = pressure (psi), L = length (ft), Q = flow (GPM)
Authority References
Our calculations are based on guidelines and standards from these authoritative sources:
- International Association of Plumbing and Mechanical Officials (IAPMO) — Uniform Plumbing Code (UPC). Learn more
- International Code Council (ICC) — International Plumbing Code (IPC). Learn more
Frequently Asked Questions
What is a good water flow rate for a house?
A residential system should deliver 6-12 GPM at fixtures. Minimum acceptable is 4 GPM.
What is max water velocity in pipes?
Max recommended velocity is 8 ft/s for copper and 12 ft/s for PVC. Excessive velocity causes erosion and noise.