PSI to HP Calculator
Convert hydraulic pressure (PSI) and flow (GPM) into horsepower — and see why PSI alone can't become HP.
PSI is pressure, not power — a sealed cylinder can hold 3,000 PSI forever while doing zero work. Power appears only when pressurized fluid flows. That's why converting PSI to horsepower always needs the flow rate in gallons per minute.
PSI to HP Formula
Why You Can't Convert PSI Alone
Pressure is force per area; power is work per time. The same 5 HP can appear as 3,430 PSI at 2.5 GPM (a log splitter) or 429 PSI at 20 GPM (a high-flow circuit). If someone quotes "PSI to HP" without flow, they're implicitly assuming a flow rate — always find out which one. The reverse question ("1 HP = how many PSI?") has no fixed answer for the same reason.
Hydraulic HP at Common Pressure/Flow Combinations
| PSI \ GPM | 5 GPM | 10 GPM | 15 GPM | 20 GPM |
|---|---|---|---|---|
| 1,000 | 2.9 | 5.8 | 8.8 | 11.7 |
| 1,500 | 4.4 | 8.8 | 13.1 | 17.5 |
| 2,000 | 5.8 | 11.7 | 17.5 | 23.3 |
| 2,500 | 7.3 | 14.6 | 21.9 | 29.2 |
| 3,000 | 8.8 | 17.5 | 26.3 | 35.0 |
Worked Example
Pressure Buys Force, Flow Buys Speed
Understanding which knob does what is the difference between specifying a system that works and one that disappoints.
| Increase this | You get | You do not get |
|---|---|---|
| Pressure (PSI) | More force at the cylinder — a heavier load lifted, a tougher log split | No extra speed. The ram moves at the same rate. |
| Flow (GPM) | Faster cylinder movement, shorter cycle time | No extra force. It will stall on the same load. |
Both cost horsepower, and they cost it equally — the formula multiplies them. Doubling either doubles the power the engine must supply. This is why a machine that "needs more grunt" and one that "needs to cycle faster" can require the same size engine upgrade for entirely different reasons.
Turning PSI Into Cylinder Force
Pressure alone does tell you something useful — just not power. It tells you force, once you know the piston area:
So a 4-inch cylinder at 2,500 PSI pushes 31,400 lb — about 15.7 short tons. That is the number that decides whether the machine can do the job. The horsepower figure decides how fast it does it, and how big an engine has to drive the pump.
| Bore | Area (in²) | Force @ 1,500 PSI | Force @ 2,500 PSI | Force @ 3,000 PSI |
|---|---|---|---|---|
| 2" | 3.14 | 4,712 lb | 7,854 lb | 9,425 lb |
| 3" | 7.07 | 10,603 lb | 17,671 lb | 21,206 lb |
| 4" | 12.57 | 18,850 lb | 31,416 lb | 37,699 lb |
| 5" | 19.63 | 29,452 lb | 49,087 lb | 58,905 lb |
| 6" | 28.27 | 42,412 lb | 70,686 lb | 84,823 lb |
Note this is the extend stroke. On retract, the piston rod occupies part of the area, so force is lower for the same pressure — typically 20–30% less depending on rod diameter.
Sizing the Engine or Motor Properly
Hydraulic horsepower is what the fluid delivers. The prime mover has to supply more, because losses stack up on the way:
- Hydraulic HP — the useful output, from PSI × GPM ÷ 1,714.
- ÷ pump efficiency — typically 0.85 for a gear pump, 0.90–0.92 for a good piston pump. This gives the shaft power the pump demands.
- Add margin — an engine running continuously at 100% of rating will not last. Sizing at roughly 80% of the engine's rated output is normal practice.
The Metric Version
Outside North America, hydraulics work in bar and liters per minute. The relationship is the same, with a different constant:
| Imperial | Metric | Conversion |
|---|---|---|
| PSI | bar | 1 bar = 14.504 PSI |
| GPM (US) | L/min | 1 US GPM = 3.785 L/min |
| HP | kW | 1 HP = 0.7457 kW |
Worth watching: a UK or imperial gallon is 4.546 liters, not 3.785. Mixing gallon definitions introduces a 20% error, which on a pump specification is the difference between adequate and stalling.
This Does Not Apply to Compressed Air
Pneumatic systems look similar — pressure and flow — but air is compressible, so the simple product of pressure and flow overstates the useful work available. Air power is normally specified in SCFM at a stated pressure, and compressor sizing follows the compression work required rather than PSI × flow ÷ 1,714. Do not use this page to size an air compressor.
Frequently Asked Questions
No — pressure alone isn't power. You need the flow rate too: HP = PSI × GPM ÷ 1,714.
There's no fixed answer — it depends on flow. 1 HP supports 1,714 PSI at 1 GPM, 343 PSI at 5 GPM, or 171 PSI at 10 GPM.
No — it gives fluid (output) power. Divide by pump efficiency (typically 0.80–0.90) to size the motor or engine driving the pump.
One gallon is 231 in³ (19.25 board-feet of work per PSI per minute). Converting gallon-PSI/min into 33,000 ft-lb/min (1 HP) yields the constant 1,714.
31,400 lb — about 15.7 short tons. Force = PSI × piston area, and a 4-inch bore has an area of 12.57 in². Retract force is 20–30% lower because the rod occupies part of the area.
Pressure buys force; flow buys speed. Raising either costs the same horsepower, because the formula multiplies them. Pick based on whether the machine stalls on load or simply cycles too slowly.
kW = (bar × L/min) ÷ 600. Watch the gallon definition when converting — a UK gallon is 4.546 L against the US 3.785 L, a 20% difference.
No. Air is compressible, so PSI × flow ÷ 1,714 overstates the useful work. Pneumatic systems are specified in SCFM at a stated pressure, and compressor sizing follows compression work instead.