How Much Force Do 50 mm and 63 mm Pneumatic Cylinders Generate at the Same Pressure?

Two pneumatic cylinders with different bore diameters do not generate the same force when operating at the same air pressure. For example, at 6 bar, a 50 mm piston bore produces approximately 1,178 N of theoretical extension force, while a 63 mm piston bore produces approximately 1,870 N. These values correspond to approximately 120 and 191 kgf respectively. Although there is only a 13 mm difference in bore diameter, the force increases by approximately 59%.

This difference is a determining factor in machine design and when evaluating the capacity of an existing system. When selecting the appropriate bore size from FENITSA products, operating pressure, direction of movement, and the actual load conditions of the application should be evaluated together with the force calculation.

Why Does Force Increase When the Piston Bore Increases from 50 mm to 63 mm?

Compressed air acts on the piston surface to generate linear force. When pressure remains constant, the force increases as the effective piston area becomes larger. However, piston area is proportional not to the diameter itself, but to the square of the diameter.

The theoretical extension force is calculated using the following formula:

F = P × π × D² / 4

In this formula, F represents force, P represents pressure, and D represents the piston bore diameter. When pressure is expressed in bar and diameter in millimeters, the following practical formula can be used to obtain the result in Newtons:

F (N) = P (bar) × π × D² (mm²) / 40

The surface area of a 50 mm piston is approximately 1,963.5 mm², while the area of a 63 mm piston is approximately 3,117.2 mm². Since the ratio between these two areas is 63² / 50² = 1.5876, the increase in theoretical extension force at the same pressure is 58.76%.

The 50 mm and 63 mm dimensions mentioned here refer to piston bore diameter; they do not indicate the piston rod diameter or the stroke length.

Force Comparison at 4, 5, and 6 Bar

The table below compares the theoretical extension forces of the two bore diameters at different operating pressures. The calculations assume that the opposite chamber is open to atmosphere and that exhaust back pressure and friction are neglected.

kgf is a unit of force; the values shown in the table should not be interpreted directly as safe lifting capacities. To move a load vertically, the system must overcome not only the weight of the load but also friction and acceleration forces.

The table also demonstrates the effect of pressure loss. For example, with a 50 mm bore, reducing the pressure from 6 bar to 5 bar lowers the theoretical extension force by approximately 196 N. For this reason, calculations should consider not only the compressor gauge pressure but also the actual pressure reaching the cylinder during movement.

Are Extension and Retraction Forces the Same?

In a single-rod, double-acting cylinder, the retraction force is lower than the extension force. This is because the piston rod reduces the effective area exposed to pressure during the return stroke.

When calculating retraction force, the piston rod area is subtracted from the piston area:

Fretraction (N) = P (bar) × π × (D² − d²) / 40

Here, d represents the piston rod diameter. Assuming, for example, that both cylinders use a 20 mm piston rod, at 6 bar:

• A 50 mm piston produces approximately 990 N of theoretical retraction force.
• A 63 mm piston produces approximately 1,682 N of theoretical retraction force.

The piston rod diameter used in this example should be verified from the technical data table of the selected model. In applications where the load is pulled during the return stroke, considering only the extension force may result in selecting a cylinder that cannot provide sufficient force.

Why Can’t the Entire Calculated Force Be Used?

Theoretical calculation is a starting point for comparing different bore diameters. During actual operation, seal friction, exhaust back pressure, pressure losses in the air line, and mechanical alignment issues can reduce the usable force. Accelerating the load to the desired speed also requires additional force.

For example, if the total force requirement of an application is 1,100 N, a 50 mm bore producing 1,178 N at 6 bar may appear theoretically sufficient. However, the difference is only 78 N. Operating losses and pressure fluctuations may eliminate this margin. In such a case, the suitability of a larger bore should be evaluated according to actual operating conditions.

You can review different bore, stroke, and series options on FENITSA’s pneumatic cylinders page and evaluate the product group that best matches the calculated force requirement.

Is a 63 mm Bore Always the Better Choice?

Although a larger bore provides more force, it also increases air consumption. At the same stroke length, the geometric volume filled during the extension stroke is approximately 59% greater with a 63 mm bore. Total cycle air consumption also depends on the piston rod diameter, operating pressure, and connection volumes.

If the existing valves and hoses cannot provide sufficient flow, increasing the cylinder bore may reduce movement speed. For this reason, a 50 mm solution that provides sufficient force may offer lower air consumption and a smaller installation footprint in suitable applications.

Selecting the correct pneumatic cylinder for FENITSA is based on determining the bore diameter that provides the required force with an adequate operating margin, maintains the target movement speed, and avoids unnecessary compressed air consumption.