If you’ve been ordering metal studs for any length of time, you’ve run into the terminology: 20 gauge, 25 gauge, 33 mil, 43 mil, etc. You may have noticed that different suppliers use different systems, and that “gauge” doesn’t always mean the same thing depending on who’s saying it. This confusion is surprisingly common — even among experienced framers — and it can lead to misspecification, failed inspections, or ordering the wrong product entirely.
Here’s a clear breakdown of what the numbers mean, how the cold-formed steel industry got here, and how to read a section designation correctly.
Before anything else, this is the single most important point in this article: gauge numbers and mil numbers run in opposite directions.
This catches a lot of framers off guard because the cold-formed steel industry has shifted from gauge to mils over the past couple of decades, but the old gauge language hasn’t gone away. Many framers — especially those who came up in the trade before the switch — say “gauge” out of habit but are mentally picturing mils. When they hear “a higher number,” they think “thicker,” because that’s how mils work. But if you ask them for “a higher gauge,” what they get is actually thinner steel.
The simple rule: if you’re holding a tape measure or thinking about thickness, you’re thinking in mils. If you’re reading a gauge number, the lower number is the thicker product.
Whenever you’re ordering, specifying, or submitting, use mils. It removes the ambiguity entirely.
For decades, steel thickness was commonly expressed in gauge numbers. The problem with gauge is that it’s an approximation — a holdover from the wire-drawing industry that doesn’t map cleanly to modern precision standards. Gauge numbers run inverse to thickness, vary by material type, and differ between industries.
The Steel Framing Industry Association (SFIA) and the American Iron and Steel Institute (AISI) standardized on mils — thousandths of an inch — as the unit for specifying cold-formed steel framing thickness. Mils give you a direct, measurable dimension rather than an index number tied to a legacy system. Industry guidance now explicitly states that gauge numbers should not be used to order, design, or specify CFS framing — mils or decimal inch are the correct units.
That said, the gauge language hasn’t disappeared from jobsite conversation. Most suppliers, including Formetal, understand what you mean when you ask for “25 gauge” or “20 gauge.” But for formal submittals, structural drawings, and engineering documents, the mil designation is what governs.
A point of confusion for framers who work across trades, or who have background in mechanical or structural construction: the word “mil” means one-thousandth of an inch in every context, but how the industry uses it as a designation differs from one product category to another.
In cold-formed steel framing, the mil designation has a specific, standardized meaning: it represents the minimum base metal thickness delivered, per AISI S100-16/S2-20. So when a stud is labeled “33 mil,” the minimum acceptable base steel thickness is 0.033″. The design thickness used by engineers in calculations is slightly higher than that (more on this below), but the mil number on the label is the minimum you should be getting.
This is different from how mil terminology shows up — or doesn’t — in other steel products:
The practical takeaway: if you’re cross-referencing thicknesses between CFS framing and another product category, don’t assume the numbers translate. Convert everything to decimal inches and verify from there.
Here are the standard cold-formed steel thicknesses available from Formetal. The mil designation is the minimum base metal thickness; the design thickness is the value engineers use in load calculations.
| Mil Designation (= minimum thickness) |
Design Thickness (in) | Reference Gauge No. |
|---|---|---|
| 18 mil | 0.0188″ | 25 |
| 23 mil | 0.0242″ | 20‑EQ (Formetal) |
| 30 mil | 0.0312″ | 20‑Drywall |
| 33 mil | 0.0346″ | 20‑Structural |
| 43 mil | 0.0451″ | 18 |
| 54 mil | 0.0566″ | 16 |
| 68 mil | 0.0713″ | 14 |
| 97 mil | 0.1017″ | 12 |
| 118 mil | 0.1242″ | 10 |
A few important notes:
The mil label IS the minimum thickness. When you order 33 mil, the steel delivered must be at least 0.0329″ — which rounds to 33 mils. The design thickness (0.0346″ for 33 mil) is what engineers use in calculations and is approximately 5.3% higher than the minimum, because AISI S100 specifies that the minimum delivered thickness must be at least 95% of the design thickness.
Note the two “20 gauge” entries. There is 20-Drywall (30 mil) and 20-Structural (33 mil). These are two different products. 20-Drywall is for nonstructural drywall framing only; 20-Structural is the entry-level structural thickness used in many load-bearing applications. If a spec says “20 gauge” without qualifying which one, ask — the difference is consequential.
What is a 20-Gauge EQ stud? EQ (equivalent) studs are interior nonstructural framing products engineered to deliver wall performance equivalent to a heavier gauge through optimized section geometry, knurling, and other manufacturing refinements — while using less steel. Formetal manufactures a proprietary 23 mil 20-Gauge EQ stud, color-coded brown for fast jobsite identification. EQ studs offer a lighter, lower-cost option for interior partitions without sacrificing the lateral wall performance contractors expect from a standard 20-gauge product. For nonstructural interior framing where weight, handling speed, and cost matter, the 20-EQ is often the right call.
Cold-formed steel members follow a standardized designation system. Once you know how to read it, the designation tells you everything about the section’s geometry and thickness. The format is:
[Web Depth][Section Type][Flange Width]-[Thickness in mils]
Let’s break down a common example: 600S162-33
So 600S162-33 is a 6-inch stud with 1-5/8-inch flanges at 33-mil thickness. That’s one of the most common structural stud sizes in commercial framing.
The industry uses the acronym STUFL to remember the five section types:
Web depths in the designation are expressed in 1/100-inch units. Here are the common conversions:
| Designation | Actual Depth |
|---|---|
| 250 | 2‑1/2″ |
| 350 | 3‑1/2″ |
| 362 | 3‑5/8″ |
| 400 | 4″ |
| 550 | 5‑1/2″ |
| 600 | 6″ |
| 800 | 8″ |
| 1000 | 10″ |
| 1200 | 12″ |
Note that 362 represents 3-5/8 inches (3.625″), not 3.62 inches. The web depth values in the designation are nominal — they refer to the actual fractional-inch dimensions, with the designation number being a rounded label rather than a literal decimal.
The middle number in the designation gives flange width in 1/100-inch units:
| Designation | Flange Width |
|---|---|
| 125 | 1‑1/4″ |
| 137 | 1‑3/8″ |
| 162 | 1‑5/8″ |
| 200 | 2″ |
| 250 | 2‑1/2″ |
| 300 | 3″ |
| 350 | 3‑1/2″ |
Thickness is a key factor — though not the only one — separating nonstructural and structural applications. Per ASTM C955, a structural member is one in a steel-framed system in which loading exceeds specific thresholds (a transverse load of 20 lbf/ft of member length, certain superimposed axial loads, etc.).
In practice:
Nonstructural framing (interior partition walls, shaft walls, soffit framing) is typically specified at 18 mil (25 gauge), 23 mil (20-EQ), or 30 mil (20-Drywall). These sections carry no gravity loads beyond the weight of attached finishes. Engineering is generally not required for standard nonstructural assemblies that fall within published prescriptive tables.
Structural framing (load-bearing walls, shear walls, exterior curtain walls) starts at 33 mil (20-Structural) and goes up from there. These sections are engineered to carry specific loads, and the structural drawings will call out the required section, thickness, and spacing.
Confusing a nonstructural stud with a 20-Structural stud in a load-bearing application is a real-world problem. Visually they look nearly identical. The section designation stamped or color-coded on the stud is your verification — always check it.
Most CFS manufacturers paint a color-coded stripe on the stud to identify thickness. The color codes used by Formetal are:
| Color | Color Name | Mil | Reference Gauge |
|---|---|---|---|
| Brown | 23 mil | 20‑EQ (Formetal) | |
| Pink | 30 mil | 20‑Drywall | |
| White | 33 mil | 20‑Structural | |
| Yellow | 43 mil | 18 | |
| Green | 54 mil | 16 | |
| Orange | 68 mil | 14 | |
| Red | 97 mil | 12 |
Color is a fast jobsite check, but it’s not a substitute for verifying the stamped designation. If a stud has no color stripe at all, that’s typically the lightest nonstructural 18 mil (25 gauge) — but again, confirm the label.
One more number you’ll encounter on product labels and specifications is the coating designation. Cold-formed steel framing is zinc-coated (galvanized) to resist corrosion, and the coating weight is measured in ounces of zinc per square foot of total steel surface (both sides combined).
When a spec calls for G90 and G60 is delivered, it’s a submittal rejection. For projects near the Gulf Coast, Atlantic coast, or in high-humidity markets like Florida and South Carolina, G90 is typically required.
When ordering or specifying cold-formed steel framing:
If you’re pulling from a set of drawings, the structural notes or framing schedule will typically list the section designation, spacing, and coating — those three pieces of information define your order. When in doubt, call your supplier and give them the designation from the drawings. That’s the most reliable way to make sure you’re getting exactly what the engineer of record specified.
The Formetal Company manufactures cold-formed steel studs and track in Forest Park, Georgia, and supplies framers and contractors throughout the Southeast. If you have questions about specifying the right product for your project, contact our team — we’re happy to help you work through it.