Hydraulic Cylinder Force Calculator
Push and pull force, speed and flow demand from bore, rod and pressure.
How it works
Force is pressure times area, and a cylinder has two different areas. On the extend stroke the fluid pushes on the full bore. On the retract stroke it pushes on the bore minus the rod — the annulus — so a cylinder always pulls less hard than it pushes, and always retracts faster for the same flow.
extend force = P × π D² ÷ 4
retract force = P × π (D² − d²) ÷ 4
That asymmetry is a design tool rather than a nuisance. A 2:1 rod is chosen precisely so retract is half of extend and twice the speed, which suits a machine that does work in one direction and returns empty. It is also why a regenerative circuit exists: feed the rod-side oil back into the bore side and the cylinder extends fast at reduced force, using the rod area alone.
Speed comes from flow, not pressure. A pump delivering 20 L/min into a 63 mm bore moves the rod at about 107 mm/s regardless of what the gauge says — pressure only rises to whatever the load demands, up to the relief setting. Slow cylinder, pressure fine: you need more flow. Weak cylinder, speed fine: you need more pressure or more bore.
The efficiency figure covers seal friction, which is real and load-dependent. It rises sharply as seals age and as side load goes up, and a cylinder that has started binding shows it here before it shows anywhere else.
Common questions
Why is the retract force lower?
The rod occupies part of the piston face, so there is less area for oil to push on. With a 63 mm bore and a 36 mm rod you lose about a third of the area, and with it a third of the force.
What rod size should I pick?
The standard ratios are 1.4:1 for general work — retract about half of extend — and 2:1 where you want a genuine 2:1 speed and force split. A thicker rod also resists buckling on long strokes, which is the other reason to go up.
How much pump do I need?
Flow sets speed: litres per minute divided by bore area gives velocity. Power is pressure times flow — 160 bar at 20 L/min is 5.3 kW of hydraulic power, so the electric motor wants to be around 7 kW after pump losses.
Does the cylinder buckle?
It can, on long strokes with the rod fully out. That is a column-buckling problem in the rod, governed by stroke and end mounting rather than by pressure; manufacturers publish stroke limit charts and they are worth respecting.