Water Pressure Calculator

This calculator estimates water pressure at a fixture by combining elevation-driven static pressure loss with friction-driven pressure loss along the supply pipe, starting from an assumed 60 PSI supply pressure. Pipe Diameter has an outsized effect on Friction Loss -- the underlying Hazen-Williams formula raises diameter to nearly the 5th power, so a 10% change in Pipe Diameter swings Friction Loss more than the same percentage change in Flow Rate or Pipe Length, even though a fraction of an inch feels like a small adjustment to make. Elevation Change plays no role in Friction Loss at all -- it only affects Pressure at Outlet directly, through a separate static-head term, and moves it in the opposite direction from what intuition might suggest for "uphill": a positive Elevation Change means the outlet sits above the source, so it subtracts from the available pressure, while a negative value (outlet below the source) adds to it.

Flow Rate and Pipe Length both raise Friction Loss as they increase, but neither swings the result as sharply as Pipe Diameter does. If Pressure at Outlet lands below roughly 20 PSI, a booster pump or a larger-diameter pipe run are the two standard fixes.