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

PSI
ft

Pipe Parameters (Hazen-Williams Friction Loss)

GPM
in
ft
% of pipe length

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.

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