Estimate pressure loss in a pipe from length and flow.
Friction in a pipe raises as flow rises and drops sharply as diameter shrinks. Converting that loss to psi shows what pressure actually reaches the fixture. Long, narrow or high-flow runs can drop pressure below a usable level, and this estimate justifies larger pipe or shorter runs.
Water Pressure Drop
Hazen-Williams style drop ≈ length x flow^1.85 / diameter^4.87
Hazen-Williams style drop ≈ length x flow^1.85 / diameter^4.87 Friction in a pipe raises as flow rises and drops sharply as diameter shrinks. Converting that loss to psi shows what pressure actually reaches the fixture.
Long, narrow or high-flow runs can drop pressure below a usable level, and this estimate justifies larger pipe or shorter runs.
This calculator takes 4 inputs: Pipe length, Flow rate, Pipe inner diameter, Start pressure. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.