Stainless Steel & Alloy Tubing Size Chart: OD, Wall Thickness, Gauge & Working Pressure (Inch + Metric)

A tubing size chart lays out, in table form, how a tube's outside diameter (OD), wall thickness, resulting inside diameter (ID), gauge (BWG) and allowable working pressure relate to one another, across both fractional-inch and metric sizes. Instrument and process tube is specified by OD × wall thickness, not by nominal bore. The OD holds steady for a given size; a heavier wall just eats into the ID. Below is a chart covering seamless and welded stainless-steel and high-nickel/CRA instrumentation tubing from 1/16" to 2" (3 mm to 50 mm) OD. It's matched to compression fittings from the same manufacturer, so a sized tube lines up cleanly with a sealing fitting and an alloy.

This reference covers instrumentation and process tubing (measured by OD), not structural steel tube, medical or hypodermic tubing, plumbing pipe (which uses nominal pipe size), or PEX/polymer tubing.

Also Known As: Tube Size Chart, Tubing Dimensions Chart & SS Tube OD/Wall Reference

Buyers and specifiers ask for this data under a dozen different names: tube size chart, tube size table, tubing dimensions chart, tubing dimension guide, tube sizing chart, tubing sizes list, stainless steel tube dimensions, SS tubing sizes, tube OD chart, tube wall thickness chart, tube gauge chart, BWG (Birmingham Wire Gauge) tube chart, tube OD-to-ID chart, metric tubing sizes, and tube size conversion (mm to inch). Some specify by material, too: 304 and 316 stainless steel tube sizes, 316L tube dimensions, 904L tubing sizes, duplex 2205 and super duplex 2507 tube sizes, and nickel-alloy tube dimensions for Inconel, Monel and Hastelloy grades. Whatever term you use, it's the same table below. The dimensional standard behind it is ASTM A269 for seamless and welded austenitic stainless tube; ASTM A213 covers alloy heat-exchanger and boiler tube instead.

How Tube Size Is Measured: OD, Wall Thickness, ID & BWG Gauge

Instrument tube gets sized by its outside diameter, or OD. Wall thickness is specified on its own, and the inside diameter follows from that: ID = OD − (2 × wall). The OD stays fixed, so thickening the wall doesn't change what size fitting will clamp onto it. It just shrinks the ID and pushes the pressure rating up. Gauge, meanwhile, is an older way of naming wall thickness. The BWG number, short for Birmingham Wire Gauge, corresponds to a decimal-inch wall, 20 BWG comes out to roughly 0.035", and 16 BWG lands around 0.065".

This differs from pipe. Pipe carries a nominal pipe size (NPS) and a schedule, and the stated size there is a nominal bore, not the true OD. Different logic entirely. A tube size chart and a pipe schedule chart aren't interchangeable. What's covered here is tube only; pipe-schedule sizing falls outside this scope. The values below follow ASTM A269 practice and standard published BWG data. Published OD and wall figures are nominal: tolerances on OD and wall thickness are per ASTM A269 (ASTM A213 for alloy tube), so a listed wall is a nominal value, and the guaranteed tube minimum wall thickness is that nominal figure minus the standard's permitted minus-tolerance. Instrument tube is often specified on a minimum-wall basis, since it's the wall that sets the pressure rating. Values follow the applicable standard and can be adjusted to requirement.

Imperial (Fractional-Inch) Stainless Steel Tubing Size Chart

Standard fractional-inch instrument tube ODs from 1/16" to 2", with a representative common wall, the resulting ID and the nearest BWG gauge. Additional wall thicknesses are available for each OD.

Common instrument walls fall in the 0.028"–0.134" range; heavier or lighter walls are available depending on service. Values follow the applicable standard, and the spec can be customized to your requirement.

Metric Stainless Steel Tubing Size Chart (mm)

Metric instrument tube runs from 3 mm to 50 mm OD, each size paired with a representative wall thickness and the ID that results. It's worth noting that metric tube isn't just an inch series relabeled; it's its own distinct OD lineup.

Tube Gauge (BWG) to Wall Thickness Reference Chart

The Birmingham Wire Gauge maps a gauge number to two wall thicknesses: decimal inches and millimeters. Below are the standard published values for common instrument walls.

Tube Size Conversion Chart: mm to Inch (and Inch to mm)

Metric and inch tubing run on separate OD series. A 6 mm tube isn't a 1/4" tube (1/4" comes out to 6.35 mm). That's why a fitting has to match the exact tube OD; you can't approximate across series.

Tube Working Pressure by Size: The Rating Method

Allowable working pressure depends on OD, wall thickness, alloy allowable stress and temperature. It isn't a single number you can read off from OD alone. The standard basis is ASME B31.3 process-piping allowable stress paired with the Barlow relationship, P = (2 × S × t) / D, where P is pressure, S is the allowable stress of the alloy at temperature, t is the wall thickness and D is the OD. An appropriate weld-joint factor applies for welded tube, along with a de-rating factor for elevated temperature. S drops as temperature climbs, so the same tube carries a lower rating hot than cold. A nickel or CRA alloy will rate differently from 316L at identical geometry, too.

That same Barlow relationship sits behind a tube burst pressure chart as well. Working pressure calculations use the code allowable stress; burst, or ultimate, pressure substitutes the alloy's tensile strength for S instead. The two figures differ by the design safety factor. A published burst number should never be treated as a working rating.

No made-up PSI numbers here. The rated allowable working pressure for any OD, wall, alloy, and temperature combination gets calculated using the standard constants built into Crestflo's tube pressure & wall-thickness calculator, or it can be supplied against your service conditions on RFQ. Figures follow the applicable standard, ASME B31.3, and can be tailored to what you need.

Which Compression Fitting Fits This Tube OD?

Tube OD determines which compression tube fitting you need, so line up the OD column in the chart above with the fitting size. Crestflo compression tube fittings are tested per ASTM F1387 for interchange. They come in single- and double-ferrule designs, in both imperial and metric, with end connections up to 2" (50 mm) OD. That's the same range this chart covers. Pick by OD using compression tube fittings, the fitting-by-tube-OD selector, or the tube fitting size chart. Want to know the difference between the two sizing systems? Check metric vs imperial tube fittings.

Materials & Standards for Instrument Tubing: 304L, 316L, 904L & Nickel/CRA Alloys

These sizes come in the full instrumentation alloy range: austenitic stainless, nickel, and corrosion-resistant grades. Each one follows its applicable dimensional standard.

ASTM A269 sets the primary dimensional specification, covering welded and seam-free austenitic stainless tube for general service. Alloy and heat-exchanger tube follow ASTM A213. Sour-service tube, by contrast, is supplied to NACE MR0175/ISO 15156 hardness limits. This page doesn't cover composition, mechanical properties or PREN; that deeper grade data lives on each material's own page. What this page does cover is dimensions. See also the ASTM A269 tubing specification, ASTM A213 and ASME B31.3.

Seamless vs Welded, Annealed & High-Purity Tubing Options

The same size chart holds true whether the tube is seamless or welded and drawn. Fully annealed, or soft, instrument tube bends and makes up on a compression fitting without cracking. That's exactly why instrumentation tube ships in the annealed condition. Pick the form based on the service at hand. Crestflo carries seamless instrument tubing, welded tubing, annealed instrumentation tubing, electropolished high-purity tube, hydraulic tubing, coiled tubing, and alloy tubing. Need help with sizing and wall selection? See tube sizing and wall thickness for a fuller walkthrough.

Why Buy Instrumentation Tubing & Fittings From Crestflo

Crestflo makes stainless and high-nickel/CRA instrumentation tubing, and it makes the compression tube fittings that clamp onto that tubing too. Tube, fitting and alloy all come from one source, with dimensional interchange proven to ASTM F1387. Crestflo is the instrumentation division of a four-decade-old, Government-of-India-recognized export house that has a Middle-East delivery track record behind it. Decades of supply-chain experience stand behind what is now a focused instrumentation brand.

• One tube-and-fitting system, imperial and metric, up to 2" (50 mm) OD, with F1387-qualified interchange.

Ready stock covers the standard items; specials get made to order. Delivery runs 6 to 8 weeks, against 20-plus weeks typical for the majors.

• Indian origin; US / European melt available on request, with full material traceability.
• Every part carries a heat number, stamped to the EN 10204 3.1 MTC standard. Need 3.2? It's available on request.
• Certified to ISO 9001, 14001, and 45001, plus PED. PMI, hydrostatic proof and burst testing, and NDT all happen in-house. Destructive testing runs through ISO/IEC 17025-accredited labs; third-party inspection is available on request.
• Small MOQ and private label for OEMs and distributors.

We Engineer Confidence, reviewed by the Crestflo Engineering Team.

Get a Cut-to-Size Instrumentation Tubing Quote

Send us your OD, wall, alloy and length, and we'll turn it into a cut-to-size quote. No minimum order on standard items. Request a quote or request a sample. The full chart above lives right in the page as HTML, and if you'd rather have it another way, our engineering team at Crestflo can send a formatted PDF, a CSV download or the printed line card on request. Reach us at sales@crestflousa.com or +1 346 594 9005 (Houston, TX). Browse the full stainless steel & alloy instrumentation tubing range, or see all instrumentation products.

Frequently Asked Questions: Stainless Steel Tubing Sizes

Related Tubing & Fitting References

• Stainless steel & alloy instrumentation tubing
• Compression tube fittings (F1387-tested)
• Select a fitting by tube OD
• Tube fitting size chart
• ASTM A269 tubing specification
• Tube sizing and wall thickness guide
• 316/316L stainless tube · 304/304L · 904L

Reviewed by the Crestflo Engineering Team