Water Pressure by Elevation & Booster Pump Calculator

How it works

Elevation loss = height × 0.433 psi/ft; residual = supply − elevation − meter − devices − friction; boost = required − residual; head (ft) = psi × 2.31; hp ≈ gpm × head ÷ (3,960 × efficiency)

Water pressure is just the weight of a column of water: every foot of rise costs 0.433 psi (2.31 feet per psi, 9.8 kPa per metre), so a fixture four storeys above the meter starts with 18 psi less before a drop is spent on friction. The residual at the highest, most distant fixture — after the meter, backflow preventer, softener and pipe friction each take their share — must still meet that fixture's minimum, typically 15–20 psi for showers and 25 psi for flushometers. When it cannot, a booster pump adds the difference, sized in feet of head at the design flow. Conversely, the ground floor of a tall building can see well over the 80 psi code maximum and needs a pressure-reducing valve, which is why high-rises are split into pressure zones.

Worked example

A 55 psi street supply feeding a fixture 42 ft up loses 18.2 psi to elevation and 22 psi to the meter, backflow device and friction, leaving 14.8 psi — 5.2 psi short of a 20 psi shower requirement. A booster adding 5.2 psi (12 ft of head) at 25 gpm needs only about 0.14 hp; in practice a 1/2 hp pump with a pressure tank, or a lower-loss backflow assembly, solves it.

Frequently asked questions