The power a hydraulic system carries is simply flow × pressure — how much fluid moves, times how hard it is pushed. That product is the hydraulic power delivered to the actuators. The motor driving the pump has to supply a bit more, because no pump is perfect: divide by the pump's efficiency to get the input power the motor must produce, the figure you actually size the drive on. From there the drive torque at the pump's running speed follows from the same power-torque relationship that governs any rotating shaft.
Reviewed: June 19, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: fluid-power power identity (P = p·Q).
The pump-power equations
The divisor 600 comes from the units: one bar acting on one litre per minute is 1.667 W, and 1000/1.667 ≈ 600 packages that into kW from L/min and bar. Overall efficiency rolls volumetric leakage and mechanical friction into one factor — typically 0.80–0.93 depending on pump type. The torque step is just the standard T = 9550·P/N applied to the input power at the pump's shaft speed.
Worked example — sizing a power pack
Scenario: A pump delivers 40 L/min at 150 bar; overall efficiency 85%, driven at 1,450 rpm.
The fluid carries 10 kW, but the motor must supply ~11.8 kW because of pump losses, so you would pick a standard 11 kW or 15 kW motor depending on duty and the relief-valve margin. At 1,450 rpm the drive shaft sees about 77.5 N·m. Push the pressure to 200 bar at the same flow and the hydraulic power jumps to 13.3 kW — pressure and flow each scale the power directly.
Frequently Asked Questions
P(kW) = Q(L/min) × p(bar) / 600. 40 L/min at 150 bar = 10 kW hydraulic output power.
Hydraulic = flow × pressure (output). Input = hydraulic ÷ efficiency (motor must supply). 10 kW at 85% → ~11.8 kW input.
Gear 80–85%, vane 80–88%, piston 88–93% overall. Drops at low flow/high pressure. 85% is a fair default.
Input power at worst-case flow/pressure, then next standard size up. 10 kW hydraulic / 0.85 ≈ 11.8 kW → 11–15 kW motor.
hp = kW ÷ 0.7457. 11.8 kW ≈ 15.8 hp. Imperial: hydraulic hp = GPM × psi ÷ 1714.