Calculate pneumatic cylinder airflow, piston area, stroke, or cycles per minute from the other three values in CFM, LPM, or m³/min.
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Pneumatic Cylinder Airflow Formula
The calculator uses piston area, stroke length, and cycles per minute to calculate pneumatic cylinder airflow. In its base calculation, area is in square inches, stroke is in inches, and airflow is in cubic feet per minute.
Rearranged formulas for solving the other missing values:
- Q = airflow in CFM
- A = piston area in square inches
- S = stroke length in inches
- N = cycles per minute
- 1728 = cubic inches per cubic foot
The airflow function calculates the cylinder volume moved per minute and converts cubic inches per minute to CFM. The piston area, stroke, and cycles per minute functions use the same relationship in reverse. If you enter metric units, the values are converted to the base units before the formula is applied, then converted back to the selected output unit.
Common Unit Conversions for Pneumatic Cylinder Airflow
| Quantity | Unit | Conversion Used |
|---|---|---|
| Area | 1 sq cm | 0.155 sq in |
| Area | 1 sq ft | 144 sq in |
| Length | 1 cm | 0.393701 in |
| Length | 1 ft | 12 in |
| Flow | 1 CFM | 28.3168 LPM |
| Flow | 1 CFM | 0.0283168 m³/min |
Airflow Inputs and What They Represent
| Input | What to Enter | Important Note |
|---|---|---|
| Piston area | Effective piston area | For the rod side of a double-acting cylinder, use bore area minus rod area. |
| Stroke | Distance traveled during one powered stroke | Use the actual working stroke, not the full cylinder length. |
| Cycles per minute | Number of stroke events per minute used in the calculation | If one machine cycle includes extend and retract, calculate each side separately if the areas differ. |
| Airflow | Volume flow rate | This is geometric cylinder flow and does not adjust for pressure, leakage, or compressibility. |
Example Calculations
Example 1: Calculate airflow
You have a piston area of 10 sq in, a stroke of 12 in, and a speed of 20 cycles per minute.
The required airflow is about 1.39 CFM.
Example 2: Calculate cycles per minute
You have 5 CFM of airflow, a piston area of 12.57 sq in, and a stroke of 6 in.
The cylinder can run at about 114.56 cycles per minute using this simplified airflow relationship.
FAQ
Does this calculate SCFM or CFM?
The formula calculates volumetric CFM from cylinder displacement. It does not automatically convert to SCFM or correct for supply pressure, atmospheric pressure, temperature, or compression effects. If you need compressor sizing, you may need to convert the cylinder air consumption to standard air conditions separately.
How do you find piston area if you only know the bore diameter?
For a round piston, calculate area from bore diameter with:
Use diameter in inches to get area in square inches. For example, a 4 in bore has an area of about 12.57 sq in.
Is the airflow the same for extend and retract on a double-acting cylinder?
No. The extend side usually uses the full bore area. The retract side uses the annular area, which is the bore area minus the rod area. If you need total air use for a full extend-retract cycle, calculate the extend volume and retract volume separately, then add them.
