What Is 1-Inch Square Steel Tubing? A Complete Guide to Sizes and Uses

One-inch square steel tubing is a hollow structural section with a nominal 1.000-inch outside dimension on each side, commonly made to the ASTM A500 specification for structural work.

Square structural tubing gets called many things — box tubing, 1 x 1 square tubing, HSS — but the nominal size describes only the outside profile, not what the tube can carry. Two pieces that both measure 1 inch square can behave completely differently depending on the wall thickness and the specification they were produced under.

What Does 1-Inch Square Steel Tubing Actually Measure?

Square tubing in the 1-inch size is sold by its outside dimension, and the wall thickness is a separate choice that changes everything about the inside profile.

ASTM A500/A500M is the core U.S. standard for cold-formed welded and seamless carbon steel structural tubing in square, rectangular, and round shapes. The 2023 edition states tubing is produced with a perimeter of 88 inches or less and a specified wall thickness of 1.000 inch or less. The Steel Tube Institute notes that the 88-inch perimeter limit means the largest square section under A500 would be 22 inches by 22 inches, and that domestically produced HSS is available up to that size.

For a 1-inch square tube, common market wall options include 0.049″, 0.065″, 0.083″, and 0.120″ — each producing a different inside dimension. Buyers searching for “1 inch box tubing” are usually looking at the same nominal profile.

How Tight Are the Tolerances?

Tolerances are tighter than most first-time buyers expect, and they matter the moment a tube has to fit inside something else.

For square and rectangular tubing in the 2.5-inch-and-under category, the permissible outside-dimension variation is ±0.020 inch, which is the bucket a 1-inch square tube falls into. Wall thickness carries its own allowance: Steel Tube Institute guidance cites a thickness tolerance of 10%, and AISC 360-16 Section B4.2 requires thickness-based calculations to use 0.93 times the nominal thickness.

That second point is the one people skip. A tube listed at 0.065″ wall should not be treated as a full 0.065″ in a design check.

What Is 1-Inch Square Steel Tubing Used For?

ASTM A500 tubing shows up in bridges, buildings, structural supports, building columns, highway signs, oil-field services, and communication towers — alongside lighter everyday jobs like framing, racks, trailer components, conveyors, machine parts, rails, and ornamental work.

The same nominal 1-inch square profile can serve a bike rack or a sign frame, but structural suitability depends on the grade, specification, and wall thickness, not the outside size alone. A 0.049″ wall and a 0.120″ wall are not interchangeable in a load-bearing application.

Shoppers comparing wall options for a specific build can review a tested roundup of 1-inch square steel tubing picks before ordering stock.

One last distinction worth holding onto: square structural tubing is not pipe. The Steel Tube Institute separates HSS and tubing terminology from pipe products, and mixing the two up leads to mismatched fittings and wrong wall assumptions. ASTM’s A500/A500M-23 specification defines the tubing scope directly. Suppliers also vary on which wall thicknesses and lengths they keep in stock, so a spec sheet alone does not guarantee local availability.