Compressed Air Pipe Sizing Calculator — SCFM & Pressure Drop

Q: SCFM or ACFM?

Size on SCFM (standardized) for capacity; ACFM (actual, at the line pressure) matters for velocity checks inside the pipe.

Q: Why cap pressure drop at ~10%?

Below that, tools still get rated pressure and the compressor is not fighting the pipe; more drop wastes energy and starves equipment.

Q: Does pipe material matter?

Smooth bore (aluminum, stainless, smooth PVC-rated for air) drops less than old galvanized steel; the table assumes reasonably smooth pipe.

Q: Do fittings count?

Yes — each elbow and tee adds equivalent length. On long or complex runs, size up one step to absorb them.

Short answerSize so pressure drop stays under ~2–3 psi per 100 ft (about 10% of system pressure total) and velocity below ~20–30 ft/s. Higher SCFM, longer runs and lower pressure all push you to a larger pipe.

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How it's calculated

Undersized air pipe wastes energy as pressure drop — every 2 psi lost costs roughly 1% in compressor power. Size the header for the peak SCFM at the lowest acceptable pressure, keep velocity moderate to limit turbulence and moisture carryover, and cap total drop at about 10% from compressor to tool.

Keep ΔP ≲ 2–3 psi / 100 ft · velocity ≲ 20–30 ft/s · size for peak SCFM at min pressure · total ΔP ≲ 10% of system psi

Worked example

100 SCFM at 100 psi, 150 ft.
1-inch is borderline; 1¼-inch keeps ΔP < 10%.

Reference tables

Approx. max SCFM at 100 psi, ≤2 psi/100 ft

Pipe (in)	Max SCFM
1/2	15
3/4	40
1	90
1-1/4	180
1-1/2	300
2	600

A number the tables do not give: at 100 psi, a 1-inch line comfortably feeds about 90 SCFM within a 2 psi/100 ft budget.

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FAQ

SCFM or ACFM?

Size on SCFM (standardized) for capacity; ACFM (actual, at the line pressure) matters for velocity checks inside the pipe.

Why cap pressure drop at ~10%?

Below that, tools still get rated pressure and the compressor is not fighting the pipe; more drop wastes energy and starves equipment.

Does pipe material matter?

Smooth bore (aluminum, stainless, smooth PVC-rated for air) drops less than old galvanized steel; the table assumes reasonably smooth pipe.

Do fittings count?

Yes — each elbow and tee adds equivalent length. On long or complex runs, size up one step to absorb them.

This page is a reference aid. Always verify against the compressor data and applicable piping standards. Figures shown are for orientation, not a stamped design.

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