In short: boosting 40 psi incoming up to 60 psi delivered, 15 ft higher, with 5 ft of friction loss, needs about 28.66 psi of boost — noticeably more than the raw 20 psi pressure gap, because elevation and friction add head the pump must also overcome. At 15 GPM and 65% efficiency, that works out to roughly 0.39 brake horsepower. Use the calculator above for your own numbers.
These figures are planning aids based on standard pump-sizing formulas. For final pump selection, check the result against the manufacturer's performance curve or consult a licensed engineer.
How to calculate booster pump pressure
A booster pump has to do more than close the gap between your incoming pressure and your target pressure. It also has to lift water to a higher point, if there is one, and overcome friction in the pipe between the pump and the point of use. Converting all three into a single head, then back into pressure, gives the true boost the pump must supply.
For a broader total dynamic head calculation that isn't scoped to reaching a target delivery pressure — a well pump, an irrigation system, or general TDH work — use the total dynamic head calculator instead. If you already know the required head and flow and just want horsepower, the pump horsepower calculator skips the pressure-target framing entirely.
Worked example. With 40 psi incoming, a 60 psi target, 15 ft of elevation and 5 ft of friction loss: the pressure gap alone is 20 psi, equivalent to about 46.22 ft of head. Add the elevation and friction: 46.22 + 15 + 5 ≈ 66.22 ft. Converting that head back to pressure gives about 28.66 psi — exactly what the calculator shows with its default values.
Design flow rate matters too. The boost pressure and head don't depend on flow rate — only the horsepower figures do. Use your actual peak design flow (not just an average), since a pump must be able to deliver the required head at that flow, not just at zero flow.
Boost pressure by pressure gap (15 ft elevation, 5 ft friction)
How much boost pressure is needed as the pressure gap between incoming and target grows, with elevation and friction loss held constant at the calculator's defaults.
| Pressure gap | Boost pressure | Head to add | BHP |
|---|---|---|---|
| 5 psi | 13.655 psi | 31.55 ft | 0.184 |
| 10 psi | 18.655 psi | 43.11 ft | 0.251 |
| 15 psi | 23.655 psi | 54.66 ft | 0.319 |
| 20 psi (default) | 28.655 psi | 66.22 ft | 0.386 |
| 25 psi | 33.655 psi | 77.77 ft | 0.453 |
| 30 psi | 38.655 psi | 89.32 ft | 0.521 |
| 40 psi | 48.655 psi | 112.43 ft | 0.655 |
Boost pressure by elevation gain (20 psi gap, 5 ft friction)
Holding the 40→60 psi pressure gap and friction constant, this shows how much elevation alone adds to the required boost.
| Elevation gain | Boost pressure | Head to add | BHP |
|---|---|---|---|
| 0 ft | 22.164 psi | 51.22 ft | 0.298 |
| 10 ft | 26.491 psi | 61.22 ft | 0.357 |
| 15 ft (default) | 28.655 psi | 66.22 ft | 0.386 |
| 20 ft | 30.819 psi | 71.22 ft | 0.415 |
| 40 ft | 39.474 psi | 91.22 ft | 0.532 |
| 60 ft | 48.129 psi | 111.22 ft | 0.648 |
| 80 ft | 56.784 psi | 131.22 ft | 0.765 |
Worked examples
Typical residential booster
28.66 psi
40 psi incoming to 60 psi target, 15 ft elevation, 5 ft friction, 15 GPM — the calculator's defaults. Needs about 0.39 brake horsepower at 65% efficiency.
Pressure gap alone, no elevation or friction
20 psi
Same 40→60 psi target with elevation and friction set to zero: the boost pressure equals the raw pressure gap exactly, confirming the formula reduces correctly.
Multi-story commercial riser
50.29 psi
45 psi incoming to a 65 psi target, 60 ft of elevation and 10 ft of friction at 25 GPM needs about 1.13 brake horsepower — a much larger pump than the residential case.
What else affects the result
Peak vs. average flow. Size to your peak simultaneous demand, not an average — a pump that meets the required head only at low flow can fall well short of your target pressure when several fixtures run at once.
Pump curve, not just one point. Centrifugal pumps deliver less head as flow increases. The figures here are a single design point; check them against the pump's full performance curve, not just its rated maximum, to confirm it holds the required head at your design flow.
Cycling and tank sizing. Most booster systems pair the pump with a small pressure tank to reduce short-cycling. That doesn't change the pressure or horsepower calculated here, but it does affect pump longevity and is worth planning alongside pump selection.
Efficiency varies with operating point. A pump's efficiency isn't constant — it peaks at one flow and head combination (its best efficiency point) and drops off to either side. Use the manufacturer's efficiency at your actual design flow and head when you have it, rather than a flat assumption.
Frequently asked questions
How do I size a booster pump for my desired pressure?
Add up everything the pump has to overcome: the head equivalent to your incoming-to-target pressure gap, (Ptarget − Pin)/(ρg), plus any elevation the water climbs from the pump to the point of use, plus friction loss in the piping between them. That total head, converted back to pressure, is what the pump needs to add — then choose a pump whose performance curve meets or exceeds that head at your design flow rate, with some margin.
What if my delivery point is above the pump?
Enter that elevation difference as a positive number — the pump has to lift the water as well as boost its pressure, so this adds directly to the required head. If the delivery point is below the pump, enter zero or a negative value; it slightly reduces the head the pump needs to add.
How is boost pressure different from the incoming-to-target pressure difference?
The raw pressure difference (target minus incoming) ignores elevation and friction, so it understates what the pump actually has to do whenever the delivery point is higher than the pump or the pipe run is long. With this calculator's defaults, a 20 psi pressure gap alone needs 20 psi of boost — but adding 15 ft of elevation and 5 ft of friction loss raises the real requirement to about 28.66 psi.
What pump efficiency should I assume?
Small residential booster pumps typically run 45–65% efficient at their best operating point; larger commercial and multistage pumps can reach 70% or more. Use a manufacturer's published efficiency at your design flow rate when you have it — the default of 65% is a reasonable planning estimate for a mid-size residential unit.
Where does the friction loss number come from?
Estimate it with the friction head loss calculator, using your actual pipe diameter, length and material between the pump and the point of use, then enter that head-loss figure here. Leaving it at zero will slightly undersize the pump for any real pipe run.
Does this calculator select a specific pump model?
No. It gives you the required head, boost pressure and brake horsepower at your design flow rate so you can compare those numbers against a manufacturer's pump curve. Pick a pump that meets or exceeds the required head at your flow rate, ideally with a reasonable margin rather than running right at the edge of its curve.
Sources & references
- Hydraulic Institute. ANSI/HI Pump Standards — hydraulic and brake power formulas.
- Karassik, I. J., Messina, J. P., Cooper, P., & Heald, C. C. (2008). Pump Handbook (4th ed.). McGraw-Hill.
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)