Compressed Air Pipe Capacity Table: Pipe Size and Volume Calculation
Compressed air flow by velocity for DN15–DN200 pipes, the volume of free air under pressure and pipe size selection from compressor output.
A compressed air pipe capacity table shows how much air a line can carry at a given velocity and how much volume the free air drawn in by a compressor occupies at working pressure. Correct pipe sizing directly affects pressure drop and energy use: in undersized lines pressure falls and the compressor has to run at a higher pressure than necessary.
On this page you will find two tables and a calculator: line capacity by pipe size and air velocity (dm³/s), the volume of free air at 4, 5 and 7 bar g, and pipe size selection from compressor output.
Free Air and Compressed Air
Compressor capacity is usually stated as free air delivery (FAD), the amount of air drawn in at atmospheric conditions. When air is compressed its volume shrinks; the volume actually flowing in the pipe is the volume at working pressure. Assuming isothermal compression:
Vcompressed = Vfree × 1.013 / (p + 1.013) (p in bar g)
For example, 100 dm³ of free air occupies 100 × 1.013 / 8.013 ≈ 12.6 dm³ at 7 bar g. FAD must therefore be converted to the flow at working pressure before sizing the pipe.
Compressed Air Capacity by Pipe Size (dm³/s)
The table below gives the actual air flow at working pressure (dm³/s) for each air velocity. Flow is velocity multiplied by the internal cross-section, so doubling the velocity in the same pipe doubles the flow.
Compressed Air Pipe Size Calculator
Actual flow = FAD × 1.013 / (p + 1.013). The recommended pipe is chosen using the approximate bores on which the table below is based. 1 m³/min = 16.67 dm³/s.| Air velocity (m/s) | DN15 | DN20 | DN25 | DN32 | DN40 | DN50 | DN65 | DN80 | DN100 | DN125 | DN150 | DN200 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 3.0 | 0.6 | 1.1 | 1.7 | 3.0 | 4.1 | 6.5 | 10.9 | 15.1 | 25.7 | 39.2 | 56.2 | 98.5 |
| 3.5 | 0.7 | 1.3 | 2.0 | 3.5 | 4.7 | 7.6 | 12.7 | 17.6 | 30.0 | 45.7 | 65.5 | 115.0 |
| 4.0 | 0.8 | 1.4 | 2.3 | 4.0 | 5.4 | 8.7 | 14.6 | 20.1 | 34.2 | 52.2 | 74.9 | 131.0 |
| 4.5 | 0.9 | 1.6 | 2.6 | 4.5 | 6.1 | 9.8 | 16.4 | 22.6 | 38.5 | 58.8 | 84.2 | 147.0 |
| 5.0 | 1.0 | 1.8 | 2.8 | 5.0 | 6.8 | 10.8 | 18.2 | 25.1 | 42.8 | 65.4 | 93.6 | 164.0 |
| 5.5 | 1.1 | 2.0 | 3.1 | 5.5 | 7.4 | 11.9 | 20.0 | 27.6 | 47.1 | 71.9 | 103.0 | 181.0 |
| 6.0 | 1.2 | 2.1 | 3.4 | 6.0 | 8.1 | 13.0 | 21.8 | 30.1 | 51.3 | 78.5 | 112.0 | 197.0 |
| 6.5 | 1.3 | 2.3 | 3.7 | 6.5 | 8.8 | 14.1 | 23.7 | 32.6 | 55.6 | 85.0 | 122.0 | 213.0 |
| 7.0 | 1.4 | 2.5 | 4.0 | 7.0 | 9.5 | 15.1 | 25.5 | 35.1 | 59.9 | 91.5 | 131.0 | 230.0 |
| 7.5 | 1.5 | 2.7 | 4.3 | 7.5 | 10.1 | 16.2 | 27.3 | 37.6 | 64.2 | 98.0 | 140.0 | 246.0 |
| 8.0 | 1.6 | 2.8 | 4.5 | 8.0 | 10.8 | 17.3 | 29.1 | 40.1 | 68.5 | 105.0 | 150.0 | 263.0 |
| 8.5 | 1.7 | 3.0 | 4.8 | 8.5 | 11.5 | 18.4 | 31.0 | 42.6 | 72.8 | 111.0 | 159.0 | 278.0 |
| 9.0 | 1.8 | 3.2 | 5.1 | 9.0 | 12.2 | 19.5 | 32.8 | 45.1 | 77.1 | 118.0 | 169.0 | 296.0 |
Approximate bores on which the table is based: DN15 ≈ 16 mm, DN20 ≈ 21.3 mm, DN25 ≈ 26.9 mm, DN32 ≈ 35.7 mm, DN40 ≈ 41.5 mm, DN50 ≈ 52.5 mm, DN65 ≈ 68.1 mm, DN80 ≈ 79.9 mm, DN100 ≈ 104.4 mm, DN125 ≈ 129 mm, DN150 ≈ 154.4 mm, DN200 ≈ 204.4 mm.
Example: Sizing a Compressor Main
A compressor with an FAD of 6 m³/min (100 dm³/s) runs at 7 bar g. The actual flow at working pressure is 100 × 1.013 / 8.013 ≈ 12.6 dm³/s. In the 6 m/s row of the table a DN50 line carries 13.0 dm³/s, so a DN50 main is sufficient for this compressor at about 6 m/s.
Volume of Free Air Under Pressure (dm³)
| Free air volume (dm³) | Compressed air volume (dm³) | ||
|---|---|---|---|
| 4 bar g | 5 bar g | 7 bar g | |
| 5 | 1.01 | 0.84 | 0.63 |
| 10 | 2.02 | 1.68 | 1.26 |
| 15 | 3.03 | 2.52 | 1.9 |
| 20 | 4.04 | 3.37 | 2.53 |
| 25 | 5.05 | 4.21 | 3.16 |
| 30 | 6.06 | 5.05 | 3.79 |
| 35 | 7.07 | 5.89 | 4.42 |
| 40 | 8.08 | 6.73 | 5.06 |
| 50 | 10.1 | 8.42 | 6.32 |
| 60 | 12.1 | 10.1 | 7.58 |
| 70 | 14.1 | 11.8 | 8.85 |
| 80 | 16.2 | 13.5 | 10.1 |
| 90 | 18.2 | 15.1 | 11.4 |
| 100 | 20.2 | 16.8 | 12.6 |
| 125 | 25.2 | 21.0 | 15.8 |
| 150 | 30.3 | 25.2 | 19.0 |
| 175 | 35.3 | 29.5 | 22.1 |
| 200 | 40.4 | 33.7 | 25.3 |
| 225 | 45.4 | 37.9 | 28.4 |
| 250 | 50.5 | 42.1 | 31.6 |
| 275 | 55.5 | 46.3 | 34.8 |
| 300 | 60.6 | 50.5 | 37.9 |
| 350 | 70.7 | 58.9 | 44.2 |
| 400 | 80.8 | 67.3 | 50.6 |
| 500 | 101.0 | 84.2 | 63.2 |
| 750 | 151.0 | 126.0 | 95.0 |
| 1000 | 202.0 | 168.0 | 126.0 |
| 1250 | 252.0 | 210.0 | 158.0 |
Values are based on isothermal compression and an atmospheric pressure of 1.013 bar.
Frequently Asked Questions
Is the flow in the table free air or compressed air?
The pipe capacity table gives the actual air flow in the line at working pressure. Convert the compressor FAD to working pressure with the second table or the formula before using it.
Why is velocity limited in compressed air lines?
Friction loss rises roughly with the square of velocity. High velocity causes pressure to fall at the end of the line, forces the compressor to run at a higher pressure and increases energy consumption; it also carries moisture and dirt further along the line.
How do I convert m³/min to dm³/s?
1 m³/min = 1000 dm³ / 60 s = 16.67 dm³/s. For example, an FAD of 3 m³/min equals 50 dm³/s.
Conclusion
To size a compressed air line, first convert the compressor output to working pressure, then pick the pipe size that keeps velocity within limits. The tables and calculator let you do both steps quickly. For air preparation units, valves and fittings, see our pneumatic equipment product group.
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