What Thickness or Size of DOM Tubing Do You Need? (Roll Cage OD/Wall/ID Guide)

Roll cage tubing is specified by outside diameter (OD) and wall thickness — never by inside diameter directly. Most builds land somewhere between 1.5″ and 2.0″ OD with a wall thickness of 0.083″–0.120″, and where exactly you land depends on vehicle weight and which sanctioning body’s rulebook you’re building to. The numbers below are reference ranges pulled from multiple public sources, not a substitute for your specific rulebook — treat every figure here as a starting point to verify, not a final answer.

How Tubing Is Sized (and Why ID Is Never the Starting Point)

Every rulebook and supplier specifies tubing as OD × wall thickness. Inside diameter is a calculated result, not an independent spec:

ID = OD − (2 × wall thickness)

Example: 1.75″ OD tubing with a 0.095″ wall has an ID of 1.75 − (2 × 0.095) = 1.56″. If you’re comparing two tubes with the same OD but different wall thickness, the thicker-wall tube is both stronger and has a smaller ID — that trade-off is unavoidable.

Reference Sizes by Application

These are reference ranges assembled from public rulebook summaries and fabrication guides, not a copy of any single official rulebook. Vehicle weight, sanctioning body (SCCA, NASA, NHRA/SFI, FIA, Ultra4, SCORE), and even whether the vehicle is street-driven or purpose-built race-only all shift these numbers. Confirm against your specific class’s current rulebook before you buy tubing or build a cage — the organizations differ from each other, and rules change over time.

DOM vs. 4130 Chromoly: How Material Choice Changes the Size

DOM and chromoly aren’t priced or sized the same way for equivalent strength:

Because chromoly’s higher strength-to-weight ratio lets a builder use a smaller diameter or thinner wall for the same strength target, rulebooks that permit the substitution usually require documentation proving the equivalent strength — keep material certifications on hand for tech inspection if you go this route. If you haven’t settled on DOM vs. chromoly yet, that decision should come before you’re locking in a size — see why DOM tubing costs what it does and how its strength compares for the underlying trade-off.

Pipe vs. Tube: Not the Same Thing — Use Tube

This is a distinction that matters specifically for structural fabrication, and it’s easy to get wrong if you’re shopping by price alone: pipe and tube are sized and rated differently, and they are not interchangeable for a roll cage.

• Tube is a structural member. It’s sized and rated by its actual outside diameter and wall thickness — the numbers on the label are the numbers you get.
• Pipe is a pressure vessel. It’s sized by nominal inside diameter under a schedule system, and the nominal number doesn’t match the actual inside diameter. For a given nominal size, pipe is generally weaker, heavier, and less dimensionally consistent than structural tube of a comparable size.

For any structural application — a roll cage being the clearest example — use tube, not pipe, even when pipe is cheaper and easier to find. The one narrow exception: ASTM A513 Grade B is a structural pipe with reasonable properties that shows up in recreational (non-sanctioned) builds. It’s not approved for sanctioned racing that we’re aware of, and it’s a budget floor, not a default choice.

This is also the answer to a related, frequently-searched question — “what is DOM pipe?” People searching that phrase are almost always asking about DOM tubing itself (see what is DOM tubing for the process explanation); “pipe” and “tube” get used loosely as synonyms in casual search. But if you’re actually sizing material for a build, the engineering distinction above is the one that matters.

Bend Allowance: Sizes Change Once You Bend the Tube

Two separate rules govern how much a bend is allowed to distort the tube — don’t confuse them:

• Minimum diameter at the bend. Several rulebook summaries (ARA/FIA-derived) specify that the tube’s diameter at the thinnest point of a bend must be at least 90% of the tube’s nominal OD. Example: 1.75″ tubing must measure at least 1.75 × 0.9 = 1.575″ at the tightest point of any bend.
• Ovality as a fabrication quality target. Separately, a commonly cited fabrication benchmark targets 8% or less ovality at the bend midpoint (measured as widest OD minus narrowest OD, divided by nominal OD) — this is a recommended quality target from tube-bending equipment sources, not a universal rulebook requirement, and it’s a different measurement from the 90%-minimum-diameter rule above.

Wall thickness also thins out at the outside of a bend. If your rulebook requires a 0.118″ minimum wall, ordering nominal 0.120″ (or 0.125″) stock gives you margin so the bend doesn’t measure under spec when a tech inspector checks it with an ultrasonic gauge or a drilled inspection hole.

Before You Cut Any Tube

Vehicle weight and your specific sanctioning body’s current rulebook are the two variables that actually decide your size — everything in the tables above is a starting reference, not a substitute for that document. A roll cage is a safety structure; if there’s any doubt about which size or wall thickness your build requires, confirm with your rulebook or a scrutineer before you buy material, not after you’ve bent it.

Related reading: What Is DOM Tubing? · Why Is DOM Tubing So Expensive, and Is It Stronger Than Regular Tubing? · Where to Buy DOM Tubing

Danny Ni Engineering & Mechanical Systems Writer

Danny Ni is an engineering-focused technical writer at SYZ Machine, specializing in mechanical components, linkage systems, and real-world application engineering. His work covers aftermarket vehicle parts, industrial joints, and mechanical principles, translating complex engineering concepts into practical insights for engineers, fabricators, and industry buyers.

See Full Bio