Water Pressure & PSI Loss Calculator
Calculate static water pressure from elevation head, friction pressure loss using the Hazen-Williams equation, and net pressure at any point in a water distribution or plumbing system.
System Parameters
Pipe Parameters (Hazen-Williams Friction Loss)
Formulas Used
Elevation Pressure Change:
ΔPelev (PSI) = Elevation (ft) × 0.4335 PSI/ft
(Positive elevation = uphill = pressure loss; negative = downhill = pressure gain)
Hazen-Williams Friction Loss:
hf = 0.2083 × (100/C)1.852 × Q1.852 / d4.8704 [ft head per 100 ft]
Friction Loss (PSI) = hf × Leff / 100 / 2.3077
where Q = flow (GPM), d = inside diameter (in), C = Hazen-Williams coefficient,
Leff = pipe length × (1 + fittings %/100)
Flow Velocity:
v (ft/s) = Q (ft³/s) / A (ft²) | Qft³/s = GPM / 448.831 | A = π/4 × (d/12)²
Net Outlet Pressure:
Pout = Psource − ΔPelev − ΔPfriction
Assumptions & References
- Water density assumed at 62.4 lb/ft³ (fresh water, ~60 °F); 1 PSI = 2.3077 ft of water head.
- Hazen-Williams equation is valid for turbulent flow of water at typical temperatures (40–75 °F) and is not suitable for other fluids or laminar flow.
- Minor losses (fittings, valves, bends) are approximated as a percentage of equivalent pipe length. A 10 % default is typical for simple systems; complex systems may require 20–50 %.
- Recommended residential flow velocity: 2–8 ft/s. Velocities above 8 ft/s risk water hammer and erosion.
- Typical residential supply pressure: 40–80 PSI (AWWA / IPC standard).
- Hazen-Williams C values per AWWA M51 and engineering references (Mott, Applied Fluid Mechanics).
- Formula reference: Hazen & Williams (1905); AWWA Manual M22.