Hydraulic Cylinder Force Calculator
Enter the bore diameter, rod diameter, and working pressure to find the extend and retract force of a hydraulic cylinder — in kilonewtons and kilogram-force — plus the bore and annulus areas.
Cylinder force
How the calculation works
The tool computes two areas: the full bore area for the extend stroke, and the annulus — bore area minus rod area — for the retract stroke. It converts the working pressure from bar to pascals, then multiplies pressure by area to get force in newtons, reporting it in kilonewtons and kilogram-force so it is easy to relate to a load or a lift.
Because the rod steals part of the piston face on the way back, the retract force is always the smaller of the two. The rod diameter must be less than the bore, or no annulus exists and the calculator flags it. All values are rounded for display.
Frequently Asked Questions
How does a hydraulic cylinder produce force?
A cylinder converts fluid pressure into a straight-line force. Force equals pressure times the area the fluid pushes against, so a bigger bore or a higher pressure both raise the force. Pressure is usually quoted in bar, where one bar is 100,000 pascals; multiply that pressure by the piston area in square metres and you get the force in newtons.
Why is the retract force lower than the extend force?
On the extend stroke, fluid pushes against the full face of the piston — the whole bore area. On the retract stroke, the rod takes up part of that face, so fluid only acts on the ring-shaped annulus around the rod. Because the annulus is smaller than the bore, the same pressure produces less force pulling in than pushing out. A fatter rod widens that gap.
What is the annulus area?
The annulus is the ring of piston face left exposed on the rod side once the rod is subtracted — its area is the bore area minus the rod's cross-sectional area. It sets the retract force and also the retract speed, since a smaller effective area means the same flow moves the piston faster on the way back in.
Does this include seal friction or back-pressure?
No. The figures are the ideal hydraulic forces from pressure acting on area. Real cylinders lose a little to seal friction, and back-pressure on the return line reduces net force further. Use this as a sizing estimate and derate it according to the cylinder's efficiency and your circuit's back-pressure.
Educational tool only. Results are ideal hydraulic estimates rounded for display and ignore seal friction and back-pressure; verify any figure that matters for design or safety against the cylinder manufacturer’s data.