Light Gauge Steel Keel: Gauge, Strength and Spacing

In short: A light gauge steel keel specification should define base metal thickness, steel grade, yield strength, zinc coating and stud spacing. Common grades include S280GD and S350GD, with minimum yield strengths of 280 MPa and 350 MPa. Typical stud spacing is 400 mm or 600 mm. The correct thickness depends on wall height, span, loads and deflection limits.

1. What Is a Light Gauge Steel Keel?

A light gauge steel keel is a cold-formed galvanized steel profile used to build interior partitions, exterior wall framing and suspended ceiling systems. Common profiles include C-shaped studs, U-shaped tracks, ceiling channels and furring channels.

Unlike hot-rolled structural steel, these profiles are formed from relatively thin steel coils. Their strength comes from the combination of material properties, profile geometry, flange width, lip dimensions and connection details.

A complete light gauge steel keel specification should include:

• Profile type: C stud, U track or ceiling channel.
• Nominal base metal thickness (BMT), measured in millimeters.
• Steel grade and minimum yield strength in MPa.
• Zinc coating class and coating mass.
• Stud spacing and maximum unsupported height or span.
• Applicable manufacturing and structural design standards.

2. What Is the Difference Between Steel Gauge and Thickness in mm?

Gauge is a traditional thickness designation used in some markets, especially North America. However, gauge numbers do not provide a universal thickness conversion. Different standards and product categories can assign different thicknesses to the same gauge number.

For international procurement, specifying thickness in millimeters is more reliable. For example, a 0.75 mm steel profile should be identified by its base metal thickness rather than simply calling it 22 gauge.

Two thickness measurements are important:

• Base metal thickness (BMT): The thickness of the steel substrate, excluding the zinc coating. This is the preferred value for structural calculations.
• Total coated thickness: The measured thickness including the protective metallic coating.

When comparing supplier quotations, confirm that the quoted thickness refers to BMT. A product advertised as 0.75 mm may not provide 0.75 mm of actual base steel if the supplier is quoting total coated thickness.

3. Which Steel Grade Is Best for Light Gauge Steel Keels?

Steel grade determines the minimum yield strength and influences the structural capacity of a cold-formed profile. S280GD and S350GD are common galvanized structural steel grades under EN 10346.

The following grades are relevant to light gauge steel framing:

• S280GD: Minimum yield strength of 280 MPa. Suitable for many general framing applications, subject to section design.
• S350GD: Minimum yield strength of 350 MPa. Offers higher yield strength and can improve load capacity when profile geometry and stability are properly designed.
• Q235: A Chinese carbon structural steel grade under GB/T 700. Its specified yield strength depends on product thickness. It is not automatically equivalent to S280GD or S350GD.

For galvanized cold-formed framing, S280GD and S350GD provide clear grade designations under EN 10346. If Q235 is specified, confirm its material certificate, thickness-dependent yield strength and suitability for the intended coating and forming process.

4. What Zinc Coating Should Light Gauge Steel Keels Have?

Galvanized coatings protect steel profiles against corrosion. Two common coating designations are Z120 and Z275 under EN 10346.

• Z120: Minimum total zinc coating mass of 120 g/m² across both surfaces.
• Z275: Minimum total zinc coating mass of 275 g/m² across both surfaces.

Z275 provides a heavier zinc coating than Z120 and is often considered for applications requiring greater corrosion protection. However, the correct coating depends on indoor humidity, exposure conditions, ventilation and expected service life.

For dry interior partitions, coating requirements may be less demanding than those for humid environments. Exterior wall framing and coastal projects require additional corrosion assessment. Do not assume that a heavier zinc coating alone makes a framing system suitable for every environment.

5. What Stud Spacing and Thickness Should You Choose?

Stud spacing is the center-to-center distance between adjacent vertical studs. The two common arrangements are 400 mm and 600 mm.

• 400 mm spacing: Provides more frequent support for wall boards and can improve resistance to local panel bending. It is useful for taller walls, heavier finishes and demanding service conditions.
• 600 mm spacing: Reduces the number of framing members and can lower material and installation costs. It requires suitable board thickness, fixing arrangements and stud capacity.

The following table provides preliminary thickness ranges for typical non-load-bearing partition walls. These are screening values for initial specification, not universal code minimums. They assume ordinary indoor conditions, standard board finishes and no significant additional loads.

Wall Height (m)	Stud Spacing (mm)	Indicative BMT (mm)	Steel Grade
2.4–2.7	400	0.50–0.55	S280GD
2.4–3.0	600	0.55–0.75	S280GD
3.0–3.6	400	0.60–0.75	S280GD or S350GD
3.0–3.6	600	0.75–0.95	S350GD

Actual minimum thickness must be verified through structural calculations. Stud depth, flange width, steel strength, board restraint, connection details and allowable deflection all affect the result. Taller walls may require deeper profiles, thicker steel, closer spacing or intermediate bracing.

6. How Do Span and Load Determine the Required Gauge?

Wall height and stud spacing are only two parts of the design. The unsupported span and applied loads also determine the required profile dimensions and thickness.

For partition walls, engineers should consider the following factors:

• Wall height: Increasing the unsupported height increases bending demand and deflection. A taller wall may need a deeper stud or additional support.
• Wind and lateral loads: Exterior walls must resist project-specific wind pressure and suction. Internal partitions may also need to resist specified horizontal loads.
• Attached loads: Cabinets, wall-mounted equipment, doors and heavy finishes can introduce concentrated loads that require reinforcement.
• Ceiling spans: Ceiling channels and joists must be selected according to their clear span, ceiling weight, insulation, suspended equipment and maintenance loads.
• Deflection limits: A profile may meet its strength requirement but still deflect too much. The allowable limit must follow the project specification and applicable design standard.

For North American projects, ASTM C645 covers nonstructural steel framing members, while ASTM C955 covers load-bearing steel framing members. AISI S100 provides design requirements for cold-formed steel structural members. European projects commonly refer to EN 1993-1-3 for cold-formed members and EN 10346 for continuously hot-dip coated steel products.

Designers should also check local building codes, connection capacity, local buckling, distortional buckling and overall member stability. Higher yield strength does not automatically mean that a thinner profile will perform equally well.

Quick answers

What is the common thickness of a light gauge steel keel? Common BMT values include 0.50 mm, 0.55 mm, 0.75 mm and 0.95 mm, depending on the application.

Is 400 mm or 600 mm stud spacing better? Both are common. Use 400 mm for closer support and evaluate 600 mm against wall height, board requirements and structural loads.

Is S350GD stronger than S280GD? Yes. S350GD has a minimum yield strength of 350 MPa compared with 280 MPa for S280GD under EN 10346.

Next step: Review our steel structure product range, explore our steel structure engineering solutions, or contact our team through our project and service information to discuss profile specifications, material grades and framing requirements.