Short answer: Steel studs are sized by width (how deep the wall is) and by thickness, which the industry now measures in mils but tradespeople still call “gauge.” Light non-load-bearing interior walls typically use 25-gauge (18 mil) or 20-gauge (30 mil) drywall studs. Load-bearing and curtain-wall framing uses structural studs — commonly 43, 54, or 68 mil (18, 16, and 14 gauge). Heavier gauge = stiffer, stronger, taller walls.
Every steel stud has two numbers that matter. Width (the flange-to-flange depth) determines wall thickness, stiffness, and how much insulation or plumbing fits inside — common widths are 1⅝”, 2½”, 3⅝”, 4″, and 6″. Gauge/mil thickness is how thick the steel itself is, which drives strength. A tall 6″ wall with a thin gauge can still be flimsy; a short wall in a heavy gauge can be very rigid. You choose both based on wall height and load.
| Gauge | Mils (thousandths of an inch) | Common use | Color code (tip) |
|---|---|---|---|
| 25 ga | 18 mil | Non-load-bearing interior partitions (standard drywall stud) | Black / no color (varies) |
| 22 ga | 27 mil | Taller non-load-bearing walls | — |
| 20 ga | 30 mil (“drywall”) or 33 mil (“structural”) | Tall partitions; light structural — note the two versions | White (33 mil structural) |
| 18 ga | 43 mil | Structural / load-bearing framing | Green |
| 16 ga | 54 mil | Structural — walls, jambs, headers | Yellow / Orange |
| 14 ga | 68 mil | Heavy structural / curtain wall | Orange |
Color coding follows the steel-framing industry (SFIA/SSMA) convention marked on the stud, but always confirm the printed mil designation — codes can vary by manufacturer.
The single most common ordering mistake is 20 gauge. There are two different products both called “20 ga”: a 30-mil drywall (EQ) stud and a 33-mil structural stud. They look nearly identical but are not interchangeable — the 33-mil structural version carries load and meets structural specs; the 30-mil EQ (“equivalent”) version does not. When your engineer specs “20 gauge structural,” order the 33-mil (marked, often white). When in doubt, order by mil thickness, not gauge.
For interior partition walls that only hold up drywall — offices, corridors, tenant build-outs — 25-gauge (18 mil) is the standard, with 20-gauge used where walls are tall or need extra rigidity (for example, walls with heavy tile, cabinetry, or above-ceiling height). Once a wall carries structural load — bearing walls, exterior curtain walls, walls supporting a floor or roof above — you move into structural studs (43 mil and up), and the size and gauge should come from the project engineer, because deflection and load calculations govern the choice.
Match the width to wall depth, mechanical/plumbing needs, and required height. Match the gauge to load: 25 ga for standard partitions, 20 ga for taller or heavier non-structural walls, and structural gauges only where an engineer specifies them. For any load-bearing or exterior application, follow the stamped drawings — don’t guess the gauge.
For standard interior partitions, 25-gauge (18 mil) is typical. Use 20-gauge (30 mil) for taller walls, walls carrying heavier finishes like tile, or where you want extra rigidity. Load-bearing walls require structural gauges (43 mil and up) per an engineer’s design.
“Gauge” is the traditional name for steel thickness; “mils” (thousandths of an inch) is the modern, precise measurement the industry now uses. For example, 25 gauge ≈ 18 mil and 20 gauge ≈ 30–33 mil. Because gauge can be ambiguous, order by mil thickness when precision matters.
One is a 30-mil “drywall/EQ” stud for non-structural use; the other is a 33-mil structural stud that carries load. They look similar but are not interchangeable. If your plans call for structural 20-gauge, specify the 33-mil version.
The steel-framing industry uses a color code stamped on structural studs to indicate thickness — for example green for 43 mil, yellow for 54 mil, orange for 68 mil. Codes can vary by manufacturer, so always confirm the printed mil designation on the stud.
Yes. Interior Exterior Building Supply carries standard drywall studs and structural-gauge studs and track, plus furring channel and accessories. Availability varies by branch — contact your nearest location with your sizes and gauges to confirm stock and delivery.
