1 1/2 inch steel tubing measures 1.500 inches across its actual outside diameter, while 1 1/2 inch pipe measures 1.900 inches — the two are different products that will not fit the same job.
Order the wrong one and a repair stalls, a weld fails inspection, or a bracket simply won’t seat. The confusion starts with the size name itself: tubing gets measured by what it actually is, pipe gets measured by a nominal label that only loosely relates to its real dimensions. Knowing which you have — and how to check it with calipers in about thirty seconds — prevents most of the mix-ups.
What Is 1 1/2 Inch Steel Tubing?
1 1/2 inch steel tubing is round steel tube with a true outside diameter of 1.500 inches, sold by its actual OD and wall thickness rather than a nominal pipe label. Two numbers define the part: the OD sets whether it fits an opening or socket, and the wall thickness sets the inside diameter and the tube’s strength.
A common reference chart lists 1 1/2 in tubing at 1.500 in OD with wall options such as 0.065 in, which works out to an approximate inside diameter of 1.370 in. Change the wall and the ID changes with it — a thicker wall on the same 1.500 in OD leaves a smaller hole. That’s why “1 1/2 inch tubing” alone is never a complete specification.
How Does 1 1/2 Inch Tubing Compare To 1 1/2 Inch Pipe?
They look like the same size on paper and are nothing alike in the hand. A 1 1/2 inch pipe carries a nominal size label, not a true measurement, and its actual outside diameter is 1.900 inches — four-tenths of an inch bigger than the tube.
Standard schedule tables put 1.500-inch tubing and 1.900-inch pipe side by side for a reason. Forget the label and you’ll try to slide a tube into a pipe fitting that was never sized for it, or clamp a pipe where only a tube will clear.
| Product | Actual Outside Diameter | Typical Inside Diameter |
|---|---|---|
| 1 1/2 in steel tubing (0.065 in wall) | 1.500 in | About 1.370 in |
| 1 1/2 in pipe, Schedule 40 | 1.900 in | About 1.610 in |
| 1 1/2 in steel tubing (heavier wall) | 1.500 in | Smaller than 1.370 in |
What Do The Standards And Types Actually Cover?
Steel tubing standards split by purpose, not by size name. Structural tubing and mechanical tubing share dimensions in some sizes but are made, tested, and tolerated differently — so the standard on the mill certificate matters as much as the OD.
ASTM A500 covers structural carbon steel tubing used for welded, riveted, and seamless structural shapes. Its round-tubing outside-diameter tolerance is listed as plus 0.5 percent, rounded to the nearest 0.005 in of the nominal OD — a built-in allowance you should expect on any structural tube you buy.
ASTM A513 covers electric-resistance-welded carbon and alloy steel mechanical tubing, spanning outside diameters from 0.1875 in to 12.000 in and wall thicknesses from 0.022 in to 0.650 in depending on product form. Within A513, Type 1 is hot-rolled and Type 2 is cold-rolled, with cited wall ranges of 0.065–0.250 in for Type 1 and 0.035–0.134 in for Type 2.
Round structural and mechanical tubing is sold in standard outside diameters including 1.500 in, 1.750 in, and 2.000 in, with wall options varying by grade and manufacturer. Dimensional-standard tables also list tube families such as A179, A192, A334, A335, A519, and A53 for heat exchangers, boiler service, low-temperature service, mechanical work, and pipe service. Never label a product “steel tubing” until you’ve confirmed which of these it actually meets.
If you’re replacing a worn section and comparing ready-made options, this guide to the best 1 1/2 inch steel tubing picks can save you the guesswork on sizing.
How To Measure Steel Tubing Correctly
Measure the outside diameter first, then the wall, then do one quick subtraction. Calipers give you the honest numbers in seconds — tape measures and eyeballing do not.
- Measure the outside diameter with calipers across the tube’s widest circular span. On a 1 1/2 inch tube, expect something very close to 1.500 in.
- Measure the wall thickness at the cut end with calipers or a micrometer. Square up the end so you’re measuring the steel, not a burr.
- Estimate the inside diameter by doubling the wall thickness and subtracting it from the OD. A 1.500 in tube with 0.065 in walls lands at roughly 1.370 in.
- Identify the standard, if you can, from the mill marking, order sheet, or packaging. ASTM A500 and ASTM A513 call for different tolerances and uses.
The most common mistake is treating “1 1/2 inch” as a pipe-style nominal size when it’s meant as an actual OD. For any replacement or compatibility check, confirm outside diameter, wall thickness, and specification together — the size name alone won’t get you there. One chart doesn’t cover another standard either: a 1.500 in tube, a 1.900 in pipe, and a structural tube with its own tolerance band are not interchangeable parts.
Still stuck between structural and mechanical? Match the tube to its job. Structural tubing carries loads; mechanical tubing handles moving parts and tight dimensional work; pressure piping and boiler or heat-exchanger tubing follow their own standards entirely. The right class answers sizing questions faster than any chart.
FAQs
Does 1 1/2 inch tubing fit inside 1 1/2 inch pipe?
That gap is too loose for a structural joint and shouldn’t be treated as a fit. Verify both diameters with calipers before relying on any tube-into-pipe pairing.
Why does tubing size use the outside diameter instead of a nominal number?
Tubing is manufactured and used by its real dimensions, so outside diameter and wall thickness are what buyers, fabricators, and fittings actually need to match. Pipe instead uses nominal labels tied to a schedule system with standardized outside diameters across the industry.
Can two 1 1/2 inch steel tubes have different inside diameters?
Yes. Wall thickness is the deciding factor. A heavier wall on the same 1.500-inch outside diameter narrows the bore, so tubes that look identical from the outside can pass very different amounts of fluid or accept different inserts. Always confirm the wall spec, not just the size name.
References & Sources
- ASTM International. “Standard Specification for Electric-Resistance-Welded Carbon and Alloy Steel Mechanical Tubing” Supports the A513 outside-diameter and wall-thickness ranges for mechanical tubing.
- Industrial Tube & Steel. “Tubing Specifications” Supports A500 structural tolerance figures, A513 Type 1 and Type 2 classifications, and round structural tubing size listings.
- McMaster-Carr. “1 1/2″ OD Tubing” Supports the 1.500 in outside-diameter size and wall-thickness options for 1 1/2 inch tubing.
