Sizes compressed air distribution pipework segments by pressure drop, per the Atlas Copco Compressed Air Manual (9th ed.) §3.6.3.
Tender-stage indicative. Verify final design to project spec and manufacturer guidance.
For design guidance only. Always verify with a qualified engineer.
About this compressed air pipe sizing calculator
This free compressed air pipe sizing calculator sizes distribution pipework segment by segment against a pressure-drop budget, using the method in the Atlas Copco Compressed Air Manual (9th ed.) §3.6.3. It is aimed at UK M&E and process engineers, contractors and compressed-air specifiers laying out a run from the compressor or receiver to the worst-case point of use, and picks a standard steel bore for each leg. Add each segment in path order, length, a fittings allowance and the free-air flow, and the calculator returns a bore, pressure loss and velocity for each. Everything runs in your browser. Nothing is uploaded.
How compressed air pipe sizing is calculated
Each segment's pressure loss per metre is the Atlas Copco relation Δp = 450 × qc1.85 × l ÷ (d5 × p), where qc is the free-air (FAD) flow in l/s, d the internal bore in mm and p the absolute supply pressure in bar(a). The fixed 0.10 bar pipework allowance (§3.6.3, Fig 3:36) is split equally across your segments, and the calculator selects the smallest standard BS EN 10255:2004 medium-series bore whose loss stays within its share, after adding the fittings equivalent-length allowance to the run length. Line velocity is Boyle's-law-corrected from FAD to line conditions and flagged against the 6–9 m/s BCAS/CAGI design range. The 10% whole-system loss guideline (CAGI / DOE) is shown as context, not the pass/fail check.
Frequently asked questions
Should I enter gauge or absolute pressure?
Absolute, in bar(a). That is the gauge reading plus about one atmosphere (a 7 bar(g) system is roughly 8 bar(a)). The absolute pressure appears in the denominator of the pressure-drop formula and in the Boyle's-law velocity correction.
What is FAD, and why is velocity corrected?
FAD is Free Air Delivery, the flow referenced to atmospheric conditions. Inside a pressurised pipe the same mass of air occupies far less volume, so velocity is Boyle's-law-corrected from FAD to line conditions before being compared to the 9 m/s ceiling.
Why is velocity flagged separately from pressure drop?
A bore can pass the pressure-drop budget yet still exceed the 9 m/s BCAS/CAGI maximum, high velocity carries oil and moisture into tools and increases erosion. The calculator flags those segments so you can step up a bore, even where the pressure check passes.