1 1/4 Inch Square Tubing Sizes Chart | Read The Wall Gauge

Square steel tube sold as 1-1/4 inch is 1.25 inches wide on the outside, so its true inside size depends on the wall thickness you pick.

For the full breakdown, see our best 1 1/4 Inch Square Tubing guide.

Two lengths of square tubing can carry the same size label and still fit completely different parts inside. That’s because 1 1/4 inch describes the outside dimension only, so the practical numbers on a 1 1/4 inch square tubing sizes chart are the wall options, which control inside width, weight, and strength.

If a project calls for 1-1/4 inch square tubing, the nominal outside width is 1.250 inches and that number never changes. The wall thickness is your real decision, and it decides everything else about the tube.

1.25 Inches Is The Outside, Not The Inside

Square tube is labeled by its outside width, not by any single inside dimension. A 1-1/4 inch tube measured wall to wall sits at 1.250 inches across, but the interior opening shrinks as the wall gets thicker. That’s why the same nominal size can accept one insert and reject another.

Inside width equals the outside width minus twice the wall thickness, which is how suppliers build their OD, ID, and wall relationship charts. A 0.065-inch wall leaves a 1.120-inch opening, while a 0.188-inch heavy wall leaves just 0.874 inch inside. Here are the stock walls commonly listed for 1.250 x 1.250 mechanical square tubing:

Weights assume bare steel at standard density, so supplier charts land in the same range. Saginaw Pipe’s square tubing chart lists structural 1-1/4 x 1-1/4 stock from 18 gauge to 11 gauge at 0.800 to 1.844 lb/ft, with 16 gauge at 0.06-inch wall and 1.05 lb/ft. Mechanical tube in this size is typically ASTM A513 when the wall is under 0.120 inch; structural versions are often ASTM A500 Grade B. Either can appear in a chart, so confirm which one you’re ordering.

How Do I Size An Insert Into 1-1/4 Square Tubing?

Measure the part going inside first, then pick a wall whose inside width clears it with room to spare. The insert’s outside width only needs to fit between opposite inner walls, which makes the inside width column of the chart the one that matters.

Work the formula both ways. A square post measuring 1.000 inch outside needs an inside width above 1.000, so every wall in the table clears it — barely, in the case of the 0.120 wall at 1.010 inches. A 1.06-inch insert fits the 0.095 wall and lighter, but not the heavier walls. For inside width = 1.250 - (2 x wall thickness), add about 1/16 inch of clearance so the insert slides instead of jamming.

What To Confirm Before You Order

Most sizing mistakes trace back to assuming one label equals one product. 1-1/4 inch square tubing is a nominal outside dimension, not a single wall, gauge, or inside size, so verify these four things on the listing:

• Outside dimension and wall. Confirm 1.250 inches outside and the exact decimal wall or gauge before you compare prices.
• Gauge vs. thickness. Gauge numbers vary by vendor and don’t map one-to-one with decimal walls, so use the chart each seller publishes.
• Mechanical vs. structural. ASTM A513 and A500 tube differ in how they’re made and which walls and gauges each supplier carries.
• Length and cut tolerance. Structural stock often runs 240 or 288 inches, saw cuts run about -0 to +1/8 inch, and stock lengths can vary by roughly 1/4 inch.

Prices swing too much by supplier, finish, and region to quote here, so check the live listing before ordering. When you’re ready to compare finished products, our picks for 1 1/4 inch square tubing pull together the tested options in one place, and every project benefits from confirming the inside fit before you pay.

FAQs

What is the inside dimension of 1-1/4 inch square tubing?

There is no single inside dimension because the wall decides it. A 0.065-inch wall leaves a 1.120-inch opening, while thicker 0.188-inch wall leaves 0.874 inch. Subtract twice the wall thickness from 1.250 inches to find the exact inside width for any wall you’re considering.

Is 1-1/4 inch square tube measured inside or outside?

Square tube is measured by its outside width, so 1-1/4 inch tube measures 1.250 inches across the outside faces. The inside opening is always smaller and varies with the wall thickness, so always size inserts and sleeves against the inside width column rather than the label.

How much does 1-1/4 inch square tubing weigh per foot?

Weight depends on wall thickness and whether the tube is mechanical or structural. Structural stock in common gauges runs from about 0.800 lb/ft for 18 gauge to 1.844 lb/ft for 11 gauge, with 16 gauge at roughly 1.05 lb/ft. Heavier decimal walls like 0.188 inch approach 2.7 lb/ft.