Compressed Air Pressure Drop Calculator
The pressure lost along a compressed air pipe for a given flow, length and inner diameter, the air speed inside it and the smallest pipe that keeps the loss within your limit.
Results
What this tool does
This is the empirical formula published in Atlas Copco's Compressed Air Manual for steel pipe: Δp = 450 × q^1.85 × L ÷ (d⁵ × p), with p in bar absolute at the start of the pipe. The diameter is raised to the fifth power, so halving the pipe multiplies the loss by 32; one size up is almost always cheaper than turning up the compressor to make up for it, which costs roughly 7 % more energy per extra bar. Bends, tees and valves are counted as extra metres of straight pipe, often 30 to 50 % more on a busy network. A common target is to lose no more than 0.1 bar between the compressor room and the furthest point of use.
Formula
Δp = 450 × q^1.85 × L ÷ (d⁵ × p) (q in L/s free air, L in m, d in mm, p in bar absolute)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
qf | Air flow (free air delivery) | L/s |
lp | Pipe length, fittings counted as extra metres | m |
dd | Inner diameter of the pipe | mm |
pg | Network pressure (gauge) | bar |
dpm | Pressure drop you accept | bar |
DP | Pressure drop along the pipe | bar |
PC | Drop as a share of the network pressure | % |
PE | Pressure left at the end | bar |
VA | Air speed inside the pipe | m/s |
DN | Smallest inner diameter for the drop you accept | mm |
Worked example
- Air flow (free air delivery)50 L/s
- Pipe length, fittings counted as extra metres100 m
- Inner diameter of the pipe40 mm
- Network pressure (gauge)7 bar
- Pressure drop you accept0.1 bar
- Pressure drop along the pipe0.076 bar
- Drop as a share of the network pressure1.09 %
- Pressure left at the end6.924 bar
- Air speed inside the pipe5.03 m/s
- Smallest inner diameter for the drop you accept37.9 mm
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.
- Mixing units is the most common source of error. Convert every input to the units shown next to each field before calculating.