In short: total pump head is the static lift plus friction losses plus the head equivalent of your target discharge pressure — a 20 ft lift needing 40 psi at the tap, with 8 ft of friction loss, adds up to roughly 120 ft (37 m) of head. Multiply that by flow rate and water density to get the power the pump has to produce.
These figures are planning aids based on published engineering formulas. For pump selection on a critical system, confirm against the manufacturer's pump curve or a licensed engineer.
How to calculate pump head
Total head is everything a pump has to overcome, converted into a single equivalent height of water. Three things add up:
Once you know the total head, the power a pump must produce follows directly from the hydraulic power equation, using the actual flow rate and water density:
Worked example. Lifting water 20 ft to a pressure tank that needs 40 psi, with an estimated 8 ft of friction loss in the pipe run, at 20 °C: 40 psi converts to about 92.4 ft of head at that temperature, so total head is 20 + 8 + 92.4 = 120.4 ft (36.71 m). At 15 US GPM, hydraulic power works out to about 0.340 kW (0.456 hp). At 70% pump efficiency, the motor needs to supply roughly 0.486 kW (0.652 hp) of brake power.
Why the numbers don't match the ÷2.31 rule exactly. The familiar shortcut (psi × 2.31 ≈ feet of head) assumes water near its maximum density, around 4 °C. This calculator uses the actual density at your chosen temperature, so figures at 20 °C or hotter come out very slightly higher than the shortcut would suggest — the difference is usually well under 1%.
Why each input changes the answer
Static lift is pure geometry — the vertical distance from the water source to the highest discharge point. It doesn't depend on flow rate or pipe size at all.
Target discharge pressure becomes head through P = ρgh: the denser the fluid, the less height is needed to produce the same pressure, which is why temperature and salinity shift the pressure-head component slightly.
Friction and minor losses come from water rubbing against pipe walls and fittings, and they genuinely change with flow rate and pipe diameter — this calculator asks for a single estimated allowance rather than computing it from pipe geometry. If you know your pipe run's length, diameter and material, the Total Dynamic Head Calculator works it out precisely with the Hazen–Williams equation.
Flow rate and efficiency don't change the head itself, but they set how much power it takes to produce that head — more flow at the same head needs proportionally more hydraulic power, and a less efficient pump needs more brake power to deliver the same hydraulic power.
Pressure-to-head quick reference
Common discharge pressures converted to feet of head, using the standard psi ÷ 2.31 rule (water near 4 °C, its reference density). The calculator above computes the exact figure for your chosen temperature.
| Pressure | Head (ft) | Head (m) |
|---|---|---|
| 10 psi | 23.07 | 7.03 |
| 20 psi | 46.13 | 14.06 |
| 30 psi | 69.20 | 21.09 |
| 40 psi (typical tank) | 92.27 | 28.12 |
| 50 psi | 115.34 | 35.15 |
| 60 psi | 138.40 | 42.18 |
| 80 psi | 184.54 | 56.25 |
| 100 psi | 230.67 | 70.31 |
Worked examples
Shallow well jet pump
112.4 ft head
15 ft lift, 40 psi target, 5 ft friction, 10 GPM at 65% efficiency: about 0.212 kW (0.284 hp) hydraulic, 0.326 kW (0.437 hp) brake power.
Two-story house booster
137.5 ft head
12 ft lift, 50 psi target, 10 ft friction, 12 GPM at 70% efficiency: about 0.311 kW (0.417 hp) hydraulic, 0.444 kW (0.595 hp) brake power.
Sump pump, open discharge
14.0 ft head
8 ft lift, no back-pressure, 6 ft friction, 40 GPM at 55% efficiency: about 0.105 kW (0.141 hp) hydraulic, 0.192 kW (0.257 hp) brake power.
What else affects the result
Velocity head. The energy in moving water itself (V²/2g) is usually small — a fraction of a foot — for typical residential pipe velocities, and is folded into the friction allowance here. It matters more at high velocities in narrow pipe, which the Total Dynamic Head Calculator accounts for directly.
Suction-side conditions. This calculator covers the discharge side. If the pump is pulling from a deep well or a suction lift with limited available pressure, check Net Positive Suction Head separately — running out of NPSH causes cavitation regardless of how much discharge head is available.
Pump curve, not just one number. A pump doesn't deliver a fixed head — its output head falls as flow rises, following its manufacturer curve. The head and flow calculated here describe your system's operating point; check it against the pump's actual curve before buying.
Frequently asked questions
What is pump head, in plain terms?
Pump head is the total resistance, expressed as an equivalent height of water in feet or meters, that a pump must push against to deliver water where you need it. It combines how far up you're lifting the water, the pressure you want at the outlet, and the friction the water loses moving through pipe and fittings.
How is head different from pressure (psi)?
Pressure and head describe the same physical quantity in different units. Head is pressure expressed as an equivalent column height of water, using P = ρgh. Pump manufacturers rate pumps in head (ft or m) because head, unlike psi, doesn't change with the density of the fluid being pumped — a pump curve in feet of head works the same for cold or hot water, while the psi it produces does shift slightly with density.
What's the difference between this calculator and the Total Dynamic Head calculator?
This tool gives you a quick estimate of the head and power a pump needs when you already have a ballpark friction-loss allowance. The Total Dynamic Head Calculator breaks friction loss down pipe segment by pipe segment using the Hazen–Williams or Darcy–Weisbach equations, which is worth doing once you know your exact pipe run, diameter and fittings.
Does pump head depend on flow rate?
The static, pressure and (to a first approximation here) friction components of head don't change with flow, but real friction loss increases roughly with the square of velocity, so a higher flow rate through the same pipe needs more friction head, not less. This calculator treats friction loss as a single value you supply; for a flow-dependent friction curve, use the Total Dynamic Head Calculator.
What happens if I undersize the pump head?
A pump can't produce more head than its curve allows at a given flow. If the system needs more head than the pump can deliver, flow drops below what you designed for, or the pump may not deliver at all at the target pressure. Sizing in a reasonable margin, and checking the manufacturer's pump curve at your actual flow, avoids this.
Sources & references
- Hydraulic Institute. Standards for Rotodynamic Pumps, ANSI/HI 9.6 series.
- Karassik, I. J., Messina, J. P., Cooper, P., & Heald, C. C. (2008). Pump Handbook (4th ed.). McGraw-Hill.
- Kell, G. S. (1975). Density, thermal expansivity, and compressibility of liquid water from 0° to 150 °C. Journal of Chemical & Engineering Data, 20(1), 97–105.
John Mac, PE
Water Systems Specialist · Austin, Texas
Texas-licensed Professional Engineer with 13+ years in residential water systems and 180+ completed projects. Writes and reviews the calculators on watercalculator.us. Read full bio
Texas PE (2016) · BS Civil Engineering, Hydraulics (2013)