An air-compressor cylinder contains the piston that draws in air and compresses it for delivery through an outlet valve. Its bore and stroke determine swept volume, while speed and volumetric efficiency affect the estimated air delivery. This metric calculator models one single-acting cylinder; it does not calculate pressure capability, motor power or the requirements of a particular tool.
Air Compressor Cylinder Interactive Calculator
Vary bore, stroke, RPM, and volumetric efficiency to see swept volume, theoretical displacement, delivered CFM, and piston speed.
Equation Used
Swept volume is piston area times stroke. Multiplying by rpm gives theoretical intake displacement; multiplying by the entered volumetric efficiency gives a delivery estimate on the corresponding inlet-volume basis. Clearance-gas expansion, filling and leakage influence real efficiency, but the calculator does not solve them.
- Single-acting cylinder with one charge per crank revolution.
- CFM is an inlet-referenced estimate after the entered volumetric efficiency, not compressed discharge volume or a certified free-air-delivery rating.
- Bore and stroke are converted from mm to m before calculation.
- Default dimensions are example inputs, not ratings or specifications for a commercial compressor.
Intake, compression and delivery
The crank and connecting rod move the piston within the bore. After delivery, gas remaining in the head clearance expands as the piston returns. Intake starts when the pressure difference permits the inlet valve to open. On the next forward stroke, inlet flow stops, pressure rises and the outlet valve opens against downstream pressure and valve resistance.
One cylinder face compresses air in this single-acting arrangement, so there is one intake charge per revolution. A pneumatic actuator cylinder performs the opposite energy role: supplied compressed air drives its piston. A clamping actuator is therefore not interchangeable with a compressor cylinder.
Main parts
- Bore and piston: form the variable-volume space.
- Sealing arrangement: limits leakage between piston and bore.
- Head and valves: provide the inlet, outlet and clearance space.
- Crank and rod: drive the reciprocating motion.
- Cooling and lubrication where required: manage heat and contact conditions.
The drawing’s valve timing, clearance and rod-length choice are illustrative. The inputs do not establish ring gaps, bearing clearance, head-bolt torque, operating temperature, orientation or a maintenance procedure. Those are equipment-specific.
From cylinder geometry to an air supply
Reciprocating compressors supply compressed air for tools, control systems and processes. A cylinder calculation helps explain displacement, but selection needs rated delivery at the required pressure, permitted duty and the necessary air treatment.
Several tools running simultaneously require their combined actual demand on a consistent reference basis. An assumed diversity factor is inappropriate when all are explicitly expected to operate together. Motor power, cylinder count and stage arrangement cannot be selected from displacement alone.
Refrigerant service, breathing air and medical or food-related use have additional equipment and air-quality requirements. A generic compressor drawing does not establish suitability for those applications.
Metric dimensions and CFM output
The calculator converts bore B and stroke S from millimeters to meters. Swept volume V = πB²S/4 is then in m³ per revolution. Multiplying V by 1,000,000 gives the Swept Volume card in cubic centimeters per revolution.
Theoretical Flow = V × N × 35.3146667 in ft³/min, where N is pump rpm. Delivered Flow multiplies that value by the entered volumetric-efficiency percentage divided by 100. It is an estimate at the inlet volume reference corresponding to that efficiency, not the volume occupied by the compressed gas at discharge.
Mean piston speed = 2SN/60 in m/s. The factor two counts both directions of travel in a revolution; division by 60 converts minutes to seconds. Instantaneous piston speed varies through the cycle.
There is no pressure, temperature, clearance or power input. Efficiency is supplied, not calculated. Increasing rpm scales flow arithmetically at that assumed efficiency; it does not certify a safe speed or predict temperature, duty cycle, wear or tool capacity.
For a multistage compressor, the same gas passes through successive stages at different densities. Adding stage swept volumes does not give total free-air delivery.
Worked example: an assumed metric cylinder
Enter bore 80 mm, stroke 60 mm, speed 1,000 rpm and volumetric efficiency 80%. Convert bore and stroke to 0.080 and 0.060 m.
V = π × 0.080² × 0.060 / 4 ≈ 0.000301593 m³/rev, or 301.593 cc/rev. Theoretical Flow is approximately 10.6507 CFM, and Delivered Flow is 10.6507 × 0.80 ≈ 8.5205 CFM.
Mean piston speed is 2 × 0.060 × 1,000 / 60 = 2.00 m/s. At 500 rpm, holding the entered efficiency constant, theoretical and delivered flow halve to approximately 5.3253 and 4.2603 CFM, and mean piston speed becomes 1.00 m/s.
These results do not specify an outlet pressure or establish the number of tools the machine can support. A receiver may buffer short demand peaks, but continuous average consumption still cannot exceed the actual supply.
Geometry and operating choices
| Change | Effect in this calculation | Additional questions |
|---|---|---|
| Larger bore | Swept volume grows with bore squared. | Pressure loads, cooling, structure and drive requirements. |
| Longer stroke | Volume and mean piston speed increase at fixed rpm. | Crank geometry, lubrication and operating limits. |
| Higher rpm | Flow and mean speed increase at fixed entered efficiency. | Valve response, actual efficiency, temperature and permitted speed. |
| Higher entered efficiency | Only estimated delivery changes. | Whether measured performance supports that assumption. |
Neither a cylinder type nor an oil-free description determines service life, duty, orientation limits or the air quality needed by a process.
Cylinder calculation questions
A compressor cylinder receives mechanical motion and compresses gas. A pneumatic actuator receives compressed gas and produces motion or force. The interactive model here is a compressor.
Theoretical Flow is geometric displacement per minute. Delivered Flow multiplies it by the entered volumetric efficiency. The calculator does not derive that efficiency from leakage or pressure.
No pressure is assigned by this calculation. Use rated or measured compressor delivery at the required pressure and stated reference conditions for equipment selection.
Not as independent free-air supplies. Gas compressed in the first stage enters the next stage at a different density. Stage geometry must be evaluated within the complete compression process.
No. It stores a finite amount of air over an allowed pressure range and can cover temporary peaks. It needs time and sufficient compressor capacity to recover.
That is equipment-specific. Oil-free construction or pressure lubrication alone does not establish mounting orientation, cooling or mechanical limits.
No. The calculator has no thermal, bearing or fault-diagnostic model. Compare measured behavior with the specific equipment limits and service instructions.
No. Manufacturers may publish displacement or measured delivery with stated test and reference conditions. Read the definition and operating pressure rather than assuming all CFM figures are interchangeable.
References and further reading
U.S. Department of Energy: Improving Compressed Air System Performance discusses compressor supply, demand, storage and system assessment. It is useful context for distinguishing a displacement calculation from a complete installed air system.
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