How to use the water hammer pressure calculator
Close a valve quickly and the momentum of the moving water turns into pressure. Enter the fluid density, the pressure wave speed in the pipe and the velocity before closure, and the pressure rise for an instant closure appears in psi with kPa and bar alongside, plus the same value as feet of head (meters in parentheses).
The relation applied is the Joukowsky one: the pressure rise is density times wave speed times velocity. The head is that rise divided by density times the gravitational acceleration (9.80665 m/s², 32.174 ft/s²), and because density cancels the head depends only on wave speed and velocity. Density goes in lb/ft³ or as a specific gravity (water = 1, taken as 1,000 kg/m³) and speeds in feet per second; they are converted to SI internally. Water at 62.4 lb/ft³, a 4,000 ft/s wave and 6 ft/s give about 323 psi. This is the quick version that takes the wave speed as an input, so deriving it from pipe material and wall thickness is not included. Values are as of October 2026.
Default wave speeds and fluid densities change with pipe material and temperature and were not confirmed in an authoritative source, so none are suggested and you enter your own. Wave speed derivation, critical closure time, the relief that slower closure brings and the maximum pipe pressure are not covered. This calculator is for reference and does not replace design. Review by a qualified engineer is required.
Frequently asked questions
Deriving the wave speed from pipe material and wall thickness is not covered. This is the quick version that takes the speed from your pipe data or analysis as it stands.
Critical closure time and the relief that comes from slower closure are not covered. This page calculates the maximum rise for an instant closure only.
The pressure rise is divided by density times gravitational acceleration. Density cancels, so the head depends only on wave speed and flow velocity.