How do I calculate hydraulic cylinder force?

Cylinder Force (lbs) = Pressure (psi) × Area (in²). Use our tool for blind-end and rod-end calculations, including metric conversions.

What is a good rule of thumb for reservoir size?

For open circuits, aim for 3–5 times pump flow rate in gallons. Our calculator includes this estimate.

Hydraulic Calculator Tool

Hydraulic & Fluid Power Calculator Tool – Free for Vickers/Rexroth Pumps, Cylinders & Motors

Enter values — results update live. Select units where available. Covers pressure/force, HP, torque, cylinders, motors, pumps, heat, reservoir, velocity, accumulator.

Pressure, Force & Area

Pressure unit: Force (lbs or N): Area (in² or cm²): Pressure:

Results:
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Fluid Power Horsepower / kW

Pressure unit: Flow unit: Pressure: Flow:

Power: --

Torque – Power – Speed

Torque unit: Power unit: Power: Speed (rpm): Torque:

Results:
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Cylinder Calculations

Bore (in/cm): Rod (in/cm): Stroke (in/cm): Pressure: Flow:

Piston Area: -- in² / -- cm²
Annulus Area: -- in² / -- cm²
Extend Force: -- lbs / -- N
Retract Force: -- lbs / -- N
Extend Speed: -- ft/min / -- m/min
Volume: -- gal / -- L
Extend Time: -- sec

Hydraulic Motor

Pressure (psi/bar): Displacement (in³/rev or cm³/rev): Flow (gpm/L/min): Speed (rpm): Torque (in-lbs/Nm): Power (hp/kW):

Results:
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Hydraulic Pump

Pressure (psi/bar): Displacement (in³/rev or cm³/rev): Flow (gpm/L/min): Speed (rpm): Efficiency (%): Torque (in-lbs/Nm): Power (hp/kW):

Results:
--

Heat Generation

Pressure drop (psi/bar): Flow (gpm/L/min):

Heat:
--

Reservoir Sizing (Rules of Thumb)

Pump Flow (gpm/L/min): System type:

Recommended capacity: -- gal / -- L
(3–5× flow for open stationary +10% air; 1.5–2× for mobile; 0.5–1× for closed)

Line Velocity Check

Flow (gpm/L/min): Line ID (in/mm): Line type:

Velocity: -- ft/s / -- m/s
Status: --

Accumulator Sizing (Adiabatic approx. n=1.4)

Precharge P1 (psi/bar): Max system P2 (psi/bar): Min system P3 (psi/bar): Required fluid vol Vx (in³/L):

Required accumulator size V1: -- in³ / -- L
(Polytropic n=1.4 for nitrogen adiabatic; round up to next standard size)

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Key Fluid Power Formulas & Equivalents

Quick-reference conversions and rules of thumb for hydraulic system design, troubleshooting, and part selection (e.g., seal kits for Vickers, Rexroth, Eaton/Char-Lynn pumps & motors).

Volume & Capacity

1 US gallon = 231 cubic inches
1 US gallon ≈ 3.785 liters (1 liter ≈ 0.2642 US gallons)
1 US gallon = 4 quarts = 8 pints = 128 fluid ounces
1 US gallon of water ≈ 8.34 pounds

Pressure Equivalents

1 psi ≈ 0.0689 bar (1 bar ≈ 14.504 psi)
1 psi ≈ 6.895 kPa
1 psi ≈ 2.036 inHg (inches of mercury)
1 psi ≈ 27.68 inches of water
1 atmosphere ≈ 14.696 psi ≈ 1.013 bar ≈ 29.92 inHg

Hydraulic Tricks Of The Trade

Pump drive power: ~1 hp input per 1 gpm at 1,500 psi
Idle/unloaded pump: ~5% of full-load hp
Reservoir capacity (gal) ≈ (L × W × H in inches) / 231
Oil compressibility: ~0.5% volume reduction per 1,000 psi
Water compressibility: ~0.33% volume reduction per 1,000 psi
Heat from wattage: 1 watt raises 1 gallon of oil by ~1°F per hour

Recommended Flow Velocities

Suction lines: 2–4 ft/sec
Pressure lines ≤500 psi: 10–15 ft/sec
Pressure lines 500–3,000 psi: 15–20 ft/sec
Pressure lines >3,000 psi: up to 25 ft/sec
Air-over-oil systems: ~4 ft/sec

These are general guidelines. Always verify with system specs or a qualified engineer. Use this tool as a reference when selecting hydraulic components from RestoPower.