First qualifying size
Size a Compressed Air Pipe
Pipe-only friction estimate
Enter peak simultaneous standard airflow and the equivalent length of the run. Under the default conditions, NPS 1¼ qualifies with about 0.53 psi calculated pipe loss.
Why This Size Qualifies
The selected size is checked against its immediate neighbors so the selection boundary is visible rather than hidden inside the calculator.
| Comparison | Pipe size | Calculated ID | Pipe loss | Inlet velocity | Qualifies? |
|---|---|---|---|---|---|
| Next smaller | — | — | — | — | — |
| Selected | — | — | — | — | — |
| Next larger | — | — | — | — | — |
Preliminary sizing boundary
This model estimates friction in common Schedule 40 steel pipe. Add dryers, filters, regulators, valves, hoses, quick disconnects, fittings, leaks, fouling, and demand transients separately. Verify actual bore, material pressure and temperature ratings, joining requirements, and the complete system design.
Calculated reference
Compressed Air Pipe Sizing Chart
100 psig inlet · 100 ft equivalent length · 1.00 psi allowable loss
Each row shows the smallest supported Schedule 40 steel size whose calculated pipe loss is at or below the displayed allowance. Change the inputs above to recalculate every row.
No calculated sizing rows are available for the current state.
Scroll horizontally to view additional columns and vertically to view additional rows. Column headers remain visible while scrolling.
| Recommended pipe | Calculated performance | Status | |||||
|---|---|---|---|---|---|---|---|
| NPS | DN | Nominal ID (in) | Pipe loss (psi) | Outlet (psig) | Velocity (ft/s) | ||
| 10 SCFM | NPS ½ | DN 15 | 0.622 in | 0.38 psi | 99.62 psig | 10.1 ft/s | Qualifies |
| 20 SCFM | NPS ¾ | DN 20 | 0.824 in | 0.34 psi | 99.66 psig | 11.5 ft/s | Qualifies |
| 30 SCFM | NPS ¾ | DN 20 | 0.824 in | 0.74 psi | 99.26 psig | 17.3 ft/s | Qualifies |
| 50 SCFM | NPS 1 | DN 25 | 1.049 in | 0.57 psi | 99.43 psig | 17.8 ft/s | Qualifies |
| 75 SCFM | NPS 1¼ | DN 32 | 1.380 in | 0.31 psi | 99.69 psig | 15.4 ft/s | Qualifies |
| 100 SCFM | NPS 1¼ | DN 32 | 1.380 in | 0.53 psi | 99.47 psig | 20.6 ft/s | Qualifies |
| 150 SCFM | NPS 1½ | DN 40 | 1.610 in | 0.53 psi | 99.47 psig | 22.7 ft/s | Qualifies |
| 200 SCFM | NPS 1½ | DN 40 | 1.610 in | 0.93 psi | 99.07 psig | 30.2 ft/s | Qualifies |
| 300 SCFM | NPS 2 | DN 50 | 2.067 in | 0.57 psi | 99.43 psig | 27.5 ft/s | Qualifies |
| 500 SCFM | NPS 2½ | DN 65 | 2.469 in | 0.62 psi | 99.38 psig | 32.1 ft/s | Qualifies |
| 750 SCFM | NPS 3 | DN 80 | 3.068 in | 0.44 psi | 99.56 psig | 31.2 ft/s | Qualifies |
| 1,000 SCFM | NPS 3 | DN 80 | 3.068 in | 0.78 psi | 99.22 psig | 41.6 ft/s | Qualifies |
Calculated results are not manufacturer capacity ratings. NPS is selected from a limited common Schedule 40 steel dimensional set. Actual bore, roughness, fitting geometry, corrosion, contamination, elevation, and component losses can change performance.
How to Use the Compressed Air Pipe Sizing Chart
- Estimate peak simultaneous airflow. Add the standard airflow of loads that can operate together. Do not size a main only from average compressor loading when short peaks govern the run.
- Enter inlet gauge pressure. Use the pressure available at the beginning of the evaluated pipe segment, not automatically the compressor nameplate or unload setting.
- Use equivalent length. Start with straight centerline length and add a defensible allowance for elbows, tees, valves, and other fittings from project or manufacturer data.
- Assign the pipe-only loss budget. Keep separate allowances for dryers, filters, regulators, hoses, quick disconnects, and end-use equipment.
- Review the boundary. Check the selected pipe against the next smaller size, then verify actual product bore, ratings, and system requirements.
Use maximum expected flow for the segment. The DOE sourcebook recommends sizing distribution mains for maximum flow and allowing for system growth.
How Compressed Air Pipe Pressure Drop Is Calculated
The selector uses one canonical SI calculation even when the inputs are displayed in U.S. customary units. Standard airflow is converted to dry-air mass flow, gauge pressure is converted to absolute pressure, and each supported nominal bore is evaluated from smallest to largest.
Mass flow: ṁ = ρsQs
Isothermal pipe relation: p2 = [p12 − f(L/D)G2RT]1/2
Variables used by the model
- p1, p2Absolute inlet and outlet pressures
- fDarcy friction factor from the flow regime and Colebrook–White relation
- L, DEquivalent length and calculated nominal inside diameter
- GMass flux, equal to mass flow divided by bore area
- R, TSpecific gas constant for dry air and absolute line temperature
Dynamic viscosity changes with temperature using Sutherland’s relation. The default steel roughness is 0.0018 in, matching the stated Parker TEC-15 validation basis. The calculation neglects heat-transfer detail, elevation change within the pipe, network branching, and transient storage behavior, so it is deliberately restricted to low-loss preliminary distribution sizing.
SCFM, ACFM, PSIG, and PSIA
These terms are not interchangeable. The calculator labels the reference conditions so a numerical flow value is not detached from the temperature and pressure that define it.
| Term | Meaning on this page | Common mistake |
|---|---|---|
| SCFM | Standard cubic feet per minute of dry air at 68°F and 14.696 psia | Treating it as the physical volume occupied inside a 100-psig pipe |
| Standard m³/min | The same standard mass flow displayed in SI volume units | Assuming the unit toggle changes the selected physical airflow |
| ACFM | Actual cubic feet per minute at a stated local pressure and temperature; not the direct input here | Entering ACFM as SCFM without converting the reference state |
| PSIG | Gauge pressure above local atmosphere; this is the inlet-pressure input | Using it directly in a gas-density equation |
| PSIA | Absolute pressure measured from vacuum; calculated as PSIG plus local atmospheric pressure | Adding atmospheric pressure twice |
At the default reference state, 100 SCFM is approximately 2.8317 standard m³/min. The same mass flow occupies a much smaller actual volume when compressed, which is why pressure must be part of a useful sizing chart.
Equivalent Length and Losses the Chart Does Not Include
Equivalent length converts fitting resistance into an additional length of the selected pipe. It is useful only when the fitting data and reference diameter are appropriate. A universal percentage added to every layout can hide the difference between a straight header and a compact run with many restrictive components.
Include in equivalent pipe length
- Straight pipe centerline length
- Elbows, bends, tees, reducers, and valves when supported by project data
- Other distributed fitting losses expressed for the applicable diameter
Budget separately
- Aftercoolers, separators, dryers, and filters
- Regulators, lubricators, hoses, and quick disconnects
- End-use equipment restrictions and minimum pressure
- Leaks, demand spikes, receiver response, and control-band effects
Measure before blaming the main. DOE notes that a restrictive filter, regulator, hose, or other point-of-use component can be mistaken for distribution-pipe loss. Pressure measurements at multiple locations are needed to isolate the cause.
Compressed Air Pipe Sizing Examples
Example 1: 100 SCFM Shop Header
Given: 100 SCFM, 100 psig inlet, 100 ft equivalent length, 1 psi allowable pipe loss, 68°F, and 14.696 psia atmosphere.
Result: NPS 1 fails the 1-psi limit, while NPS 1¼ produces about 0.53 psi loss, about 99.47 psig outlet pressure, and about 20.6 ft/s inlet velocity. NPS 1¼ is therefore the first qualifying size in the supported list.
Sanity check: The result covers the modeled pipe segment only. If a filter and regulator consume another 5 psi at peak flow, the point-of-use pressure is not 99.47 psig.
Example 2: Parker Validation Case
Given: 700 SCFM, 60 psig inlet, 100 ft, and 3 psi allowable pipe loss, using the same 68°F, 14.7-psia, Schedule 40 steel, and 0.0018-in roughness assumptions stated in Parker TEC-15.
Result direction: The model selects NPS 2½. NPS 2 exceeds the allowed loss, while NPS 2½ remains below it. This agrees with Parker’s example selection without reproducing or digitizing Parker’s proprietary curves.
Limitation: Agreement at a graphical checkpoint does not turn this independent calculated model into a Parker product rating or final system design.
Pressure-Drop Targets and Pipe Selection Guidance
The U.S. Department of Energy recommends sizing main lines for maximum flow with a 1–2% maximum pressure drop and allowing for growth. That is guidance for a properly designed distribution system, not permission to assign the entire system budget to pipe friction.
- Do not raise compressor pressure first. Higher discharge pressure increases compressor energy use and can increase unregulated demand and leakage.
- Preserve pressure for useful equipment. A larger pipe can reduce friction, but dryers, filters, regulators, hoses, and couplings still need their own peak-flow pressure-drop checks.
- Allow for credible growth. Replacing a header later can be far more disruptive than selecting a larger bore during the original installation.
- Treat velocity as a review value. This page reports velocity but does not impose a universal code limit; acceptable velocity depends on system layout, pressure stability, noise, contamination transport, and project practice.
Pipe Material, Schedule, and Bore Limitations
The automatic match uses common Schedule 40 steel nominal dimensions. NPS is a designation, not an actual inside diameter. Schedule 80 steel, stainless systems, copper tube, plastic pipe, and proprietary aluminum systems can have different bores, roughness, joining restrictions, temperature limits, and pressure ratings.
| Use this result for | Verify separately | Do not substitute unchanged |
|---|---|---|
| Preliminary common Schedule 40 steel bore selection | Actual product ID, tolerances, ratings, corrosion allowance, fittings, supports, and joining method | Aluminum, copper, PVC/CPVC, HDPE, stainless schedules, tubing, or proprietary modular pipe |
Sources, Model Scope, and Data Rights
Compressed Air Pipe Sizing Model 1.0 · Common Schedule 40 Dimensional Excerpt 1.0 · Source checked August 7, 2026
The page combines a limited dimensional excerpt with original calculated outputs. Source-controlled values and calculated results are kept distinct.
- U.S. Department of Energy — Improving Compressed Air System Performance, Third EditionFact Sheet 4, printed pages 31–32: maximum-flow design, pressure-drop causes, 1–2% main-line guidance, and system-level loss control.
- Parker Hannifin — TEC-15: Pipe Air FlowJanuary 1999: limited validation assumptions and checkpoints for Schedule 40 steel, 68°F, 14.7 psia atmosphere, and 0.0018-in roughness. Parker’s charts are not reproduced or digitized.
- ASME B36.10M-2022 — Welded and Seamless Wrought Steel PipeControlling dimensional-standard basis for the limited common NPS and Schedule 40 excerpt. The complete ASME table is not reproduced.
- NASA Glenn Research Center — ViscositySutherland relationship used for the temperature dependence of dry-air dynamic viscosity.
Dataset and Source-Check Details
- Publisher
- Turn2Engineering
- Primary design guidance
- DOE Sourcebook, Third Edition (2016)
- Dimensional basis
- Limited common ASME B36.10M-2022 Schedule 40 excerpt, NPS ½–8
- Source-controlled fields
- NPS, DN association, nominal OD, and nominal wall thickness used to derive ID
- Calculated fields
- Nominal ID, area, mass flow, Reynolds number, friction factor, pressure drop, outlet pressure, velocity, and first qualifying size
- Reference flow state
- Dry air at 68°F and 14.696 psia
- Model limits
- 1–5,000 SCFM; 10–250 psig; 1–5,000 ft; 32–150°F; low-loss pressure-drop restriction
- Known exclusions
- Networks, loops, transients, storage, elevation change within the run, component Cv, leaks, moisture, tolerance, corrosion, and product ratings
- Rights status
- Original calculated transformation with limited educational dimensional use; no full standards or manufacturer-chart download
- Download decision
- No bulk CSV; current visible calculated results may be copied
- Rounding
- Matching uses unrounded canonical values; displayed values are rounded for readability
- Maintenance trigger
- Recheck after source, dimensional scope, method, or CORE release changes
Frequently Asked Questions
It depends on pressure, equivalent length, allowable loss, bore, and roughness; under this page’s 100-psig, 100-ft, 1-psi default, common Schedule 40 NPS 1¼ is the first qualifying size.
This tool accepts standard flow at the stated reference condition and converts it to mass flow before calculating conditions inside the compressed pipe.
DOE gives 1–2% maximum pressure drop as main-line guidance, but the project must also reserve pressure for treatment equipment, controls, hoses, fittings, and end-use requirements.
Yes; include their resistance through defensible equivalent-length or loss-coefficient data that applies to the selected diameter and fitting geometry.
No; the automatic match uses common Schedule 40 steel nominal IDs and roughness, so other systems require their actual dimensions, ratings, and a suitable recalculation.
Compressed Air Pipe Sizing Summary
Size the evaluated segment at peak simultaneous standard airflow, use gauge pressure only at the labeled input, include fittings through a defensible equivalent length, and reserve a realistic pipe-only pressure-drop budget. The first qualifying Schedule 40 size is a preliminary bore selection—not approval of the complete compressed-air system.