You call up a supplier, ask for twenty feet of 2×2 tube, and the number comes back looking like it was generated by a random number generator. It wasn’t. Steel tube pricing is actually ruthlessly logical — it’s just that nobody explains the logic, because the confusion is profitable.
Once you understand two things, the whole thing collapses into arithmetic: sizing is a fixed system, and pricing follows weight, not length. Everything else — the surcharges, the minimums, the “call for pricing” — is noise layered on top. Let’s strip it back.
How Steel Tube Sizing Actually Works
There are two separate sizing universes and people mix them up constantly.
Tube (round, square, rectangular)
Tube is sized by its outside dimensions plus wall thickness. That’s the whole system.
- Round tube: outside diameter (OD) + wall. A “1-inch tube” has a 1-inch OD. The inside diameter is whatever’s left after you subtract two wall thicknesses.
- Square tube: outside width + wall. “2×2” means 2 inches outside, corner to corner, both directions.
- Rectangular tube: outside height x outside width + wall. “2×4” is not the same as “4×2” when you’re talking about orientation and bending strength, even though the weight is identical.
Pipe (a completely different animal)
Pipe breaks everyone’s brain the first time. Pipe is sized by nominal pipe size (NPS), which is a label, not a measurement. The actual outside diameter is fixed per nominal size and never changes — a 1-inch pipe has a 1.315-inch OD whether it’s Schedule 10 or Schedule 160. What changes is the wall.
So the same nominal size can be a drinking straw or a cannon barrel. If someone quotes you “1-inch pipe” without a schedule, the quote is meaningless.
Wall thickness is where the money hides
Wall thickness is usually specified in one of three ways, and they are not interchangeable:
- Gauge — a legacy number. 16 gauge is 0.0598″, 14 gauge is 0.0747″, 11 gauge is 0.120″, 10 gauge is 0.134″.
- Decimal inches — 0.120″, 0.250″, etc.
- Schedule — pipe only.
Here’s the trap: gauge numbers are not consistent across product families. Steel sheet gauge, galvanized gauge, and tube gauge don’t always line up. And “11 gauge” means something different depending on which standard the mill is running. Always confirm the decimal thickness in writing before you commit.
The Only Price Metric That Matters
Steel is sold by weight. Tube is sold by length. That mismatch is exactly where people lose money.
The trade convention for tube weight per foot, round product, is roughly:
Weight per foot = 10.69 × wall × (OD − wall) (wall and OD in inches)
For square and rectangular tube, you approximate using the mean perimeter — add up the outside dimensions, subtract roughly four times the wall for the corners, multiply by wall and the density constant. The result is close enough to sanity-check a quote.
Why this matters: a 2x2x0.120″ tube and a 2x2x0.065″ tube look identical on the rack but the thicker one weighs about 80% more. If you’re comparing quotes on “20 feet of 2×2 tube,” you might be comparing two completely different products.
Random lengths vs. cut-to-length
Mills ship random lengths, typically somewhere in the 20 to 24 foot range. Distributors buy those, then cut to your spec. That cut is a separate charge, and it’s often where the margin lives. A shop that quotes you the same price whether you want full random lengths or fifty one-foot pieces is either eating cost or hiding it.
What Actually Moves the Price
- Raw material index. Mill pricing tracks scrap and ore markets, and it moves in monthly announcements, not continuously. If you ask for a quote that holds for 30 days, you’re asking them to gamble on the index.
- Alloy. Carbon steel is the baseline. Galvanized adds coating cost. Stainless can run three to eight times carbon, and it has its own surcharge tied to nickel content.
- Manufacturing route. Welded (ERW) is cheapest and fine for most structural work. Drawn-over-mandrel gives tighter tolerances and better surface. Seamless costs the most and exists for pressure and critical applications.
- Specification. A structural spec, a mechanical spec, and a pressure spec are three different quality regimes. The spec often adds more to the price than the size does.
- Quantity. Full bundles get bundle pricing. Break a bundle and you’re paying for handling.
- Processing. Cut, drilled, notched, chamfered, painted, laser-cut — each is a line item.
- Documentation. Mill test reports and traceability paperwork are often billed separately, especially on small orders.
Then there’s the stuff that never makes the quote: freight (steel is heavy, and freight scales with weight, not value), fuel surcharges, minimum order penalties, restocking fees if you return it, and “handling” charges that appear only on the invoice.
How to Compare Quotes Without Getting Played
You can’t compare two quotes on price alone. Normalize them.
- Ask for the weight per foot, in writing. Any legitimate supplier has this on the spec sheet.
- Back out price per pound. Price divided by (weight per foot × length). Now every quote is in the same units.
- Ask whether the price is firm or “mill base plus surcharge.” The second one is a variable, not a price.
- Ask what shipping and cut charges are, separately. Bundling them into one number is how quotes get fuzzy.
- Confirm the decimal wall thickness, not the gauge number.
- Confirm the spec and the tolerances. Ten percent wall variation is normal and legal in a lot of structural specs. If you need tight, you pay for tight.
- Ask about minimum order and whether partial lengths are available.
Do this once and you’ll immediately see who’s quoting you the real number and who’s quoting you a number designed to be beaten down later.
Workarounds That Genuinely Save Money
- Remnants and drops. Fabrication shops accumulate short cutoffs they’ll never use and will often sell them by weight at a fraction of new stock. If your project doesn’t need 20-foot continuous lengths, this is the single biggest win available.
- Scrap and surplus yards. Surplus structural tube shows up constantly from canceled jobs. You’re buying mystery history, so inspect for bends, rust pitting, and mystery welds.
- Buy random lengths and cut it yourself. Trading a cut charge for an abrasive blade and twenty minutes is almost always worth it.
- Ask the counter, not the website. Posted online prices are frequently list prices with a healthy multiple baked in. Phone and counter quotes are often lower, and repeat buyers get better numbers than first-timers.
- Buy the next size up in a thinner wall. A larger OD with a thinner wall can hit the same stiffness for less weight, and weight is what you’re paying for.
- Time your order. Mill price announcements hit on a cycle. Buying right after a decrease, or locking in before an increase, is a real, predictable edge.
The Quick Version
Sizing is outside dimensions plus wall — except for pipe, which lies to you on purpose. Gauge numbers are unreliable, so use decimals. Price is weight, not length. Every quote should be convertible to a price per pound before you compare it to anything. Freight, cutting, surcharges, and minimums are the real battleground, not the headline number.
Do the arithmetic once on a real quote and the mystery evaporates. Steel pricing isn’t complicated — it’s just deliberately unexplained, because the person who understands the weight math is a lot harder to mark up.