A 1 1/2 inch aluminum tube means outside diameter in round stock, but side length in square stock, so the same number describes two different parts.
For the full breakdown, see our best 1 1/2 Inch Aluminum Tubing guide.
Order the wrong shape and the tube arrives unusable, because the number 1 1/2 does different work depending on the profile. Round tubing calls that figure the outside diameter. Square tubing calls it the side. Rectangular tubing calls it one leg of two, so a bare 1.5-inch rectangular order is incomplete and no supplier can fill it.
Three numbers decide fit: outside dimension, wall thickness, and the inside dimension the first two produce.
How Round And Square Tubing Are Measured
Round aluminum tubing is specified by outside diameter and wall thickness; square and rectangular tubing by outside width or height plus wall thickness. That distinction explains most ordering mistakes.
Same outside diameter, different bore — a bushing, bolt, or insert that fits one will rattle in the other.
Square stock is measured across the flat sides, not corner to corner. Ask for “1.5-inch diameter square tube” and you’ll get a question back, because square tube has no diameter.
Rectangular tubing needs two side dimensions, typically listed as 1 x 1-1/2 in x 0.095 in wall or 1 x 2 in x 0.125 in wall. A single number leaves the second leg undefined.
Common Sizes, Walls, And What They Cost
Wall thickness controls both strength and weight.
Round tube offers more off-the-shelf options.
| Profile | Typical Listed Size And Wall | How It’s Measured |
|---|---|---|
| Round, 6061-T6 | 1-1/2 in OD x 0.065 in wall (1.370 in ID) | Outside diameter |
| Round, 6061-T6 extruded | 1.5 in OD x 0.188 in wall (1.124 in ID) | Outside diameter |
| Square, 6063 | 1-1/2 in x 1-1/2 in x 0.060 in wall | Side length |
| Rectangular, 6063-T5 | 1 x 1-1/2 in x 0.095 in wall | Two side lengths |
| Rectangular, 6063-T5 | 1 x 2 in x 0.125 in wall | Two side lengths |
| Rectangular, 6063-T5 | 1-1/2 x 3 in x 0.120 in wall | Two side lengths |
| Round, price example | 1-1/2 in OD x 0.065 in wall, sold by the inch | Outside diameter |
Pricing tracks alloy, wall, and cut length more than profile. To compare cut-to-length sellers and ready sizes side by side, the tested lineup of 1 1 2 inch aluminum tubing options covers stock lengths and wall choices.
What Decides Whether Your Part Fits
Inside dimension, alloy, and cutting tolerance decide fit — the labeled outside size alone tells you little.
- Inside diameter: the same 1.5 in OD round tube can have a 1.370 in or 1.124 in bore depending on wall.
- Alloy: 6061-T6 is structural and weldable; 6063 extruded profiles are common for square and rectangular stock and finish cleaner.
- Shape: never swap a round 1.5 in tube for a 1.5 in square tube — one is a diameter, the other a side length, and they are not interchangeable.
- Tolerances: inventory pages note cutting tolerances and by-the-inch sales, so plan a small allowance and finishing room.
One safety note: 6061 aluminum is not recommended for exhaust systems, so for a manifold or exhaust run, pick a different alloy.
One Habit That Prevents Every Wrong Order
Write the full spec before buying: profile, outside dimension(s), wall, alloy, and temper. “1-1/2 in OD round, 0.065 in wall, 6061-T6” is an order anyone can fill. “1 1/2 inch aluminum tubing” is a coin flip.
Add the inside dimension you need and the length you want cut, and nothing is left to guess. Thomasnet’s standard-size tables are a useful cross-check before ordering.
FAQs
Does a 1 1/2 inch square tube measure 1 1/2 inches across the corners?
No. Square tubing is measured across the flat sides, so a 1-1/2 in x 1-1/2 in tube has 1.5-inch faces. Corner-to-corner distance is longer. Ordering by the diagonal gets you a smaller tube than planned.
Can I use round tube dimensions to order square stock?
No. Round tubing uses outside diameter; square and rectangular use outside side lengths. A 1.5-inch round tube has a 1.5-inch diameter; a 1.5-inch square tube has 1.5-inch sides. They are different parts — never substitute one dimension set for the other.
Why is a 1.5-inch rectangular tube listing considered incomplete?
Rectangular tubing is defined by two side dimensions plus wall thickness — for example, 1 x 1-1/2 in x 0.095 in wall. With only one number, the second leg is undefined, so a supplier cannot tell which profile you need.
References & Sources
- Hydro. “Aluminum Tubing.” Supports how square and rectangular profiles are sized versus round tubing.
- Thomasnet. “Standard Aluminum Tubing Sizes.” Source for standard round, square, and rectangular sizing conventions.
- McMaster-Carr. “Aluminum Square Tubing.” Reference for stocked square tube size and wall options.
