The gauge of a steel stud is its thickness. It affects how much load and wall height a stud can handle, what the wall costs, and how much material you handle on site. This guide explains how gauge relates to mils, which gauge suits which kind of wall, and when the choice needs an engineer instead of a chart.
Gauge vs. Mils: Start With the Right Unit
Gauge is a legacy sheet-metal designation: the lower the gauge number, the thicker the steel. Mils (thousandths of an inch) is the unit the North American cold-formed steel standard (CSA S136 / AISI S100) references, and Ontario drawings and submittals increasingly specify thickness in mils. Both appear on job sites, so this is the conversion to keep at hand:
| Gauge | Design thickness (mils) |
|---|---|
| 25 | 18 mils |
| 22 | 27 mils |
| 20 (drywall) | 30 mils |
| 20 (structural) | 33 mils |
| 18 | 43 mils |
| 16 | 54 mils |
| 14 | 68 mils |
| 12 | 97 mils |
The critical distinction: 20 gauge exists in two versions. Drywall 20 gauge (30 mils) is non-structural, and structural 20 gauge (33 mils) is not. Always confirm the mils.
Which Gauge for Which Wall
- Interior, non-load-bearing partitions: 25 gauge (18 mils) is the usual choice for offices, corridors and apartment demising walls. 22 gauge (27 mils) or drywall 20 gauge (30 mils) suits taller partitions and impact areas.
- Light load-bearing and exterior infill: structural 20 gauge (33 mils).
- Load-bearing walls and curtain wall framing: 18 gauge (43 mils) and 16 gauge (54 mils).
- Heavy structural and mid-rise framing: 14 gauge (68 mils) and 12 gauge (97 mils).
These are typical uses, not a specification. The final choice depends on the wall, as the next two sections explain.
Gauge Is Only One of Four Factors
How tall a steel stud wall can go depends on four things working together: stud gauge, stud spacing (12″, 16″ or 24″ on centre), the deflection criterion for the finish (L/120, L/240 or L/360), and the design load. Moving to closer spacing is often a cheaper fix than moving up a gauge, and a rigid finish such as tile needs a tighter deflection limit than standard drywall. Our steel stud limiting heights guide shows how much a single variable can change the result.
When the Choice Needs an Engineer
A catalogue or chart is not enough for:
- load-bearing or structural walls, which need an engineer’s stamp
- exterior curtain wall backup framing, which has to resist the actual wind loads for the site
- rigid or heavy finishes such as stone or heavy tile
- tall walls, roughly 12 to 14 feet and above
- anything going into a submittal package
Also check local building code requirements before you settle on a gauge.
Balancing Strength, Cost and Weight
Thicker steel is stronger but heavier and more expensive. The practical target is the lightest gauge that still meets the engineered requirement. Before moving up a gauge, check whether tighter spacing or a different deflection criterion solves the problem.
How to Specify Gauge on an Order
Write the mils next to the gauge, for example “20 gauge (33 mils)”, so there is no room for interpretation at the plant. Include the stud width, flange size, length and quantity as well. Saturn Metal lists every manufactured width, gauge and stock length in the steel stud and track size chart, and profiles can also be produced in custom widths, gauges or lengths. Browse steel studs, including interior steel studs and track and structural steel studs and track, or request a quote with your sizes, gauges and quantities.
Frequently Asked Questions
What is the difference between gauge and mils?
Gauge is a legacy sheet-metal number where a lower number means thicker steel. Mils are thousandths of an inch and are what the cold-formed steel standard references. For example, 25 gauge is 18 mils and 12 gauge is 97 mils.
Which gauge is used for interior non-load-bearing walls?
25 gauge (18 mils) is the usual choice for interior partitions. Taller walls and impact areas may call for 22 gauge (27 mils) or drywall 20 gauge (30 mils).
Is 20 gauge always the same thickness?
No. Drywall 20 gauge is 30 mils and non-structural, while structural 20 gauge is 33 mils. Always confirm the mils on a load-bearing wall.
