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Free engineering tool

Hydraulic power and line calculator

Enter the pressure and flow rate to see the required motor power, the flow velocity in the line, and the recommended hose/port inner diameter. You can also check the flow increase created by the oil returning from the rod side.

Line type
Required motor power 0 kW ≈ 0 HP · hydraulic power 0 kW
Flow velocity in the line 0 m/s Recommended range: 4–6 m/s
Suitable

Recommended min. inner diameter (this line)
Ø 0 mm
Area ratio φ = A / Ar
0
Flow leaving the piston side on retraction
0 L/min
Port velocity at this flow
0 m/s
Recommended min. port for return
Ø 0 mm
Line cross-section area
0 cm²
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Flow velocity recommendations are general engineering values and vary with line length, bends and oil viscosity.

Formulas used

Hydraulic power: Ph (kW) = p (bar) × Q (L/min) / 600  ·  Motor power: Pm = Ph / η  ·  1 kW ≈ 1.341 HP

Flow velocity: v (m/s) = Q (L/min) / (6 × A cm²)  ·  Required inner diameter: d (mm) = √(4 × Q / (6 × v × π)) × 10

Return flow: On retraction the oil leaving the piston side Qout = Q × φ (φ = A / Ar) — is larger than the flow entering the rod side; size the return port and valve accordingly.

How do you calculate pump motor power?

Hydraulic power is found by multiplying pressure by flow rate: P (kW) = p (bar) × Q (L/min) / 600. To account for pump and motor losses, this value is divided by the overall efficiency (typically 80–90%). For example, at 200 bar and 60 L/min, the hydraulic power is 20 kW, and with 85% efficiency the required motor power is approximately 23.5 kW.

Why does hose diameter matter?

In narrow hoses and ports, flow velocity increases, which leads to pressure loss, heating, and noise. The general recommendation is a flow velocity of 4–6 m/s in the pressure line, 2–3 m/s in the return line, and 0.6–1.2 m/s in the suction line. When a double-acting cylinder retracts, the oil leaving the piston side is greater than the pump flow by the area ratio; the return port must be selected accordingly.

Frequently asked questions

What is the formula for hydraulic pump motor power?
Motor power (kW) = pressure (bar) × flow rate (L/min) / (600 × efficiency). Efficiency is typically taken as 0.8–0.9.
How do you choose the hydraulic hose diameter?
The required cross-section is calculated from the flow rate and the recommended flow velocity: aim for 4–6 m/s in the pressure line and 2–3 m/s in the return line, then select the next standard hose diameter up.
Why does more oil return when the cylinder retracts?
During retraction, oil enters on the rod side and exits from the piston side. Because the piston-side area is larger, the outgoing flow equals the incoming flow multiplied by the area ratio (φ).
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