Hydraulic Cylinder Force and Flow Calculator (Bar, kN, lbf, L/min)
Hydraulic force is pressure times area. This calculator turns bore, rod and pressure into push and pull force in kN and lbf, and tells you how much oil flow the pump must deliver to hit a chosen speed.
Your numbers
Inside diameter of the cylinder barrel.
Piston rod diameter, which reduces the annular area on the retract stroke.
Pressure at the cylinder port. 1 bar = 0.1 MPa = 14.5 psi.
Seal friction and back pressure losses. 85 to 95 percent is common.
Target extend speed, used to size flow.
Your results
Ideal static calculation. Real force is reduced by seal friction, back pressure and acceleration. Check rod buckling and pressure ratings of the cylinder before use.
Push and pull force (kN) vs pressure (bar)
Sweeps Working pressure from 10 to 350, holding your other inputs fixed.
Equipment specs in your maintenance system
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How to use it
Enter the bore and rod diameters from the cylinder nameplate or datasheet, the working pressure at the port, an efficiency and your target piston speed. The tool outputs the push area, the smaller annular pull area, both forces and the extend-stroke flow. The chart sweeps pressure so you can see how much force each additional bar buys, and where you meet the pressure rating of the cylinder or the relief valve setting.
- Use the working pressure, not the relief setting, for normal duty
- The retract stroke is always weaker because of the rod
- Use 90 percent as a starting efficiency
- Convert lbf to tons by dividing by 2,000
The formulas
Force equals pressure times piston area. With pressure in bar, 1 bar equals 0.1 N per mm2, so a 80 mm bore has an area of about 50.3 cm2 and at 160 bar gives roughly 80 kN before losses. The pull stroke uses the annular area, bore squared minus rod squared. Flow in L/min equals area in mm2 times speed in mm/s times 60 divided by one million. Pressure drop through lines and valves lowers the pressure actually available at the cylinder.
Worked example
A cylinder with an 80 mm bore, 45 mm rod at 160 bar and 90 percent efficiency produces about 72 kN on push, roughly 16,300 lbf, and about 56 kN on pull. To extend at 100 mm/s the flow demand is about 30 L/min. If the pump delivers only 20 L/min, expect speed near 66 mm/s. Doubling pressure doubles force but not speed, which is set by flow and area alone, so size the pump and the cylinder for different jobs.
Common mistakes and ERP notes
Typical mistakes are using the relief valve setting as the operating pressure, forgetting the rod area on retract, and ignoring rod buckling on long strokes. For buyers, replacing a cylinder with a different bore changes force and flow, so record the full specification on the equipment record. In ERP maintenance modules such as SAP PM, Infor EAM or Epicor, store bore, rod, stroke and pressure rating as equipment characteristics so spares purchasing matches the right seal kit.
- Check stroke length against buckling charts
- Record the seal kit part number on the BOM
- Verify pressure rating before raising system pressure
Frequently Asked Questions
How do I convert bar to kN of force?
Multiply pressure in bar by 0.1 to get N per mm2, then by piston area in mm2 to get newtons, then divide by 1,000 for kN. For an 80 mm bore at 160 bar that is about 80 kN before efficiency losses.
Why is pull force lower than push force?
On retract the oil acts on the annular area, which is the piston area minus the rod area. A thicker rod gives a smaller pull area and lower force at the same pressure, but it also resists buckling better.
What determines cylinder speed?
Speed equals flow divided by area. Pressure sets force, not speed. A bigger bore needs more flow to move at the same speed, so for faster motion increase pump flow or use a smaller bore.
Is this enough to size a hydraulic press?
It gives a first estimate of tonnage, but a real design must add safety factors, pressure drops, duty cycle, frame stiffness and relevant machine safety standards. Use the result for screening and checking datasheets.
If cylinder specs and seal kits are not linked to your equipment BOMs, we can help structure that data in your maintenance system.
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