Square Tubing Common Sizes | What’s Actually In Stock

Steel projects usually stall at the gap between the size in your head and what a supplier actually stocks. Knowing common market sizes before you ask for a quote fixes that gap. This piece sorts out the common widths, wall thicknesses, and lengths that repeat across US supplier price lists, so your next order matches what yards keep in the rack.

What Counts As A Common Square Tubing Size?

A common size is any width a US supplier carries in regular stock rather than special order.

Wall options change with width. Here is the pattern you will see on US stock lists:

Not every width comes in every gauge — small mechanical sizes hug the light end, while structural sizes start around 11 ga. For heavier gate and kennel-run frames, 2-1/2 inch is a structural sweet spot, and our roundup of the best 2-1/2 inch square tubing options we’ve tested can save you the sourcing search.

Wall Thickness And Gauge Change The Whole Spec

Wall thickness separates light mechanical tube from structural square tube of the same width, so never order by nominal size alone.

Sellers sort square stock into two classes. Tubing under 2 inches with walls thinner than 0.120 inch usually falls under ASTM A513, a mechanical specification. Sizes 2 inches and up with 0.120-inch-or-heavier walls are typically ASTM A500 structural square HSS, Grade B. TB Tube’s tables use the same split, and the Steel Tube Institute’s ASTM A500 resource is the authority behind them.

Wall thickness also changes what you can build. A 1-inch tube in 18 ga weighs and carries far less than the same in 11 ga, and the inside opening shrinks by twice the wall. Confirm grade, size, and wall before any load-bearing use; cutting and welding behavior depend on the same specs.

Square Pipe Vs Square Tubing: The Specs To Confirm

Square pipe and square tubing are not interchangeable, and neither is every square tube automatically structural. Small sizes and thin walls are often A513 mechanical stock, so confirm which spec you are quoting before a project depends on it.

Four checks keep an order honest. First, specify outside width, wall gauge or thickness, and grade — not just “square pipe.” Second, ask whether the stock is mechanical or structural when the project carries real load. Third, verify wall thickness yourself instead of trusting nominal size. Fourth, confirm the length fits standard 20, 24, 40, or 48-foot stock before adding cutting fees.

In practice, a complete request reads: “2-1/2 inch square tube, 11 ga, ASTM A500 Grade B, 20 feet, cut to two 10-foot pieces.” That gets a yes or no from any supplier in one call, and it is the spec to have on paper before welding, drilling, or setting the first post.