# Pneumatic Cylinder Bore

> Source: https://rodlesspneumatic.com/resource-center/pneumatic-glossary/cylinder-bore/
> Language: en-US
> Category: Cylinder sizing

## Definition

Pneumatic cylinder bore is the inside diameter of the cylinder barrel associated with the piston area. Because piston area equals πd²/4, a small increase in bore produces a much larger increase in theoretical force and air consumption. Bore is therefore a force-and-capacity decision, not simply an outside-size measurement.

## Key facts

- **Core relationship:** Area = π × bore² ÷ 4
- **Selection effect:** Force and air use rise with bore squared
- **Do not confuse:** Bore size is not the cylinder body's outside diameter

## How bore changes cylinder force

Theoretical extension force is pressure multiplied by the full piston area. Retraction force is lower on a single-rod cylinder because the rod occupies part of the pressurized area. Real available force is lower again after friction, seal drag, pressure losses, load angle, and the desired operating margin are considered.

A bore should be selected from the required force at the cylinder's minimum available pressure, not from the compressor setpoint or a nominal catalog pressure alone.

## Why the smallest workable bore is not always the best choice

A cylinder sized too close to the theoretical requirement can stall as supply pressure fluctuates or friction changes. Oversizing, however, increases compressed-air demand, valve and tubing flow requirements, impact energy, and often the physical envelope.

- Use a documented load or force margin appropriate to the machine and failure consequence.
- Check both extension and retraction where the rod-side force matters.
- Recheck valve flow, tube size, cushioning, and mounting loads after changing bore.

## Bore does not prove interchangeability

Two cylinders with the same bore and stroke can still differ in mounting dimensions, overall length, port thread, rod-end thread, sensor groove, cushioning, allowable side load, and working-pressure range. ISO 15552 aligns selected dimensions for its stated cylinder family; it does not make every catalog cylinder universally interchangeable.

## What to verify before selection

- Required push and pull force
- Minimum pressure at the cylinder inlet
- Load direction and friction
- Duty cycle and target speed
- Mounting and envelope limits
- Valve, tube, and exhaust flow capacity

## Common mistakes

- Using compressor pressure instead of pressure available at the actuator
- Applying full piston area to retraction force
- Choosing bore without checking air consumption and stopping energy

## Frequently asked questions

### Does a larger bore always solve a cylinder-force problem?

No. It can add force, but low local pressure, an undersized valve or tube, binding, side load, or poor mounting can still prevent reliable motion.

### Should bore be selected from extension force or retraction force?

Check both. A single-rod cylinder has less effective area and therefore less theoretical force on retraction.

## Technical references

- [ISO 15552:2018 — Pneumatic cylinder dimensions](https://www.iso.org/standard/66921.html): Basic, mounting, and accessory dimensions for detachable-mounting cylinders from 32 mm to 320 mm bore.
- [ISO 5598:2020 — Fluid power vocabulary](https://www.iso.org/standard/67985.html): International vocabulary reference for fluid power systems and components.