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Steel Sheet Thickness Guide: How to Choose the Right Gauge and Millimetre Size

Choosing the correct steel sheet thickness can affect almost every part of a project, including strength, weight, forming, welding, appearance and cost. A sheet that is too thin may bend, vibrate or become damaged during use. A sheet that is unnecessarily thick may increase material costs, handling difficulty and overall project weight.

The challenge is that buyers may see steel thickness described in either millimetres or gauge. While millimetres provide a direct measurement, gauge numbers can be confusing because a higher gauge generally represents a thinner sheet. Gauge values may also differ between steel, stainless steel and aluminium.

This steel sheet thickness guide explains how millimetres and gauge measurements work, which factors influence material selection and what information to provide when requesting a quote.

What Does Steel Sheet Thickness Mean?

Steel sheet thickness is the distance between the two flat surfaces of the material. In Australia, thickness is commonly specified in millimetres.

For example:

• 0.6 mm steel sheet is relatively thin

• 1.0 mm steel sheet provides greater stiffness

• 1.6 mm steel is commonly considered for general fabrication

• 2.0 mm and thicker material may be selected where more strength or rigidity is needed

However, thickness alone does not determine whether a sheet is suitable. The steel grade, unsupported span, load, shape, fabrication process and operating environment must also be considered.

A flat sheet can flex more than the same material formed into a fold, channel or rib. Adding bends, returns or reinforcing sections may improve stiffness without requiring a major increase in thickness.

What Is Sheet Metal Gauge?

Gauge is a traditional system used to describe sheet metal thickness. Instead of giving the measurement directly in millimetres, it assigns a gauge number to a particular thickness.

The main point to remember is:

A lower gauge number generally means thicker sheet metal, while a higher gauge number generally means thinner sheet metal.

This can feel counterintuitive. A 16-gauge steel sheet is normally thicker than a 20-gauge steel sheet.

Gauge should not be treated as a universal measurement. The physical thickness associated with a gauge number can vary depending on whether the material is:

• Mild steel

• Galvanised steel

• Stainless steel

• Aluminium

• Another non-ferrous metal

That is why a steel gauge chart cannot always be used to select aluminium sheet thickness. When ordering material, confirming the required thickness in millimetres is usually clearer and reduces the risk of misunderstanding.

Gauge vs Millimetres: What Is the Difference?

Millimetres provide a direct measurement. If a steel sheet is listed as 1.6 mm, the specified nominal thickness is immediately clear.

Gauge is an indirect reference system. A gauge number must be checked against the correct conversion table for the selected material.

For Australian projects, specifying sheet metal thickness in millimetres is generally the more practical approach because:

• It is easier to understand

• It supports accurate quotations

• It reduces conversion mistakes

• It aligns with metric drawings and specifications

• It makes comparing different materials easier

A sheet metal gauge-to-mm chart can still be useful when reviewing imported drawings, older specifications or equipment documentation that uses gauge values. Before ordering, the converted measurement should be confirmed with the supplier.

Steel Sheet Thickness Selection Guide

There is no single thickness that suits every project. The correct choice depends on how the material will be used, supported, formed and exposed.

Thin Steel Sheet

Relatively thin sheet is often considered for applications where low weight, easy forming and appearance are more important than carrying heavy loads.

Possible applications include:

• Covers

• Liners

• Flashings

• Decorative panels

• Light enclosures

• Non-structural components

• Protective skins

Thin material is easier to cut and bend, but it may distort during welding or flex across wide unsupported areas.

General-Purpose Steel Sheet

Mid-range steel sheet thicknesses may be suitable for many fabrication jobs where a balance between formability, strength and cost is required.

Typical uses may include:

• Cabinets

• Trays

• Brackets

• Guards

• Equipment panels

• Workshop components

• Light fabricated assemblies

The exact thickness should be selected according to the component’s dimensions, load, folds and attachment points.

Heavy Sheet and Steel Plate

Thicker material is normally considered when the component must resist higher loads, impact, wear or deformation.

Possible applications include:

• Heavy brackets

• Base components

• Structural fabrication

• Machinery parts

• Industrial platforms

• Reinforcing plates

• High-wear applications

At a certain thickness, suppliers may describe the product as steel plate rather than sheet. The terminology can vary by supplier and product range, so buyers should focus on the actual millimetre thickness, grade and specification.

What Steel Sheet Thickness Should I Use?

To answer “What steel sheet thickness do I need?”, consider the following factors.

1. Purpose of the Component

Start by defining what the steel must do.

A decorative cover has different requirements from a load-bearing bracket. A machine guard may need impact resistance, while a cabinet panel may mainly need sufficient stiffness to hold its shape.

Ask:

• Will the component carry weight?

• Will people stand or walk on it?

• Will it experience vibration?

• Could it be struck by tools, vehicles or equipment?

• Is it decorative or functional?

• Is failure likely to create a safety risk?

The more demanding the application, the more important it is to obtain engineering or fabrication advice.

2. Size and Unsupported Span

A large flat panel can flex even when made from a moderately thick sheet. A smaller panel made from the same material may remain rigid.

Consider:

• Overall width and length

• Distance between supports

• Location of fasteners

• Number of folds

• Presence of frames or stiffeners

• Openings cut into the sheet

Increasing thickness is one solution, but adding folds, ribs or supports may provide better stiffness with less weight.

3. Steel Grade

Two steel sheets with the same thickness may not perform identically if they have different grades or mechanical properties.

The selected grade can affect:

• Strength

• Formability

• bending performance

• Weldability

• surface quality

• suitability for structural use

Do not select material using thickness alone when the project has structural, pressure, safety or certified-grade requirements.

4. Fabrication Method

The intended fabrication process can influence the most suitable thickness.

Cutting

Laser cutting, plasma cutting, guillotining and other processes have different capabilities and edge-quality considerations.

Bending

Thicker sheets require more force and may need larger bend radii. The grade and grain direction can also affect bending behaviour.

Welding

Very thin steel can distort or burn through if heat is not controlled. Thicker material may require different weld preparation, energy input or preheating depending on the grade and joint.

Drilling and Fastening

The material must be thick enough to support the selected fastener or connection method. In some cases, nuts, inserts, backing plates or welded connections may be required.

5. Weight

Increasing thickness increases the weight of the sheet.

Weight matters when considering:

• Manual handling

• Transport

• Delivery

• lifting equipment

• supporting structures

• moving components

• vehicle or machinery weight

The thickest option is not automatically the best. A well-designed thinner component with bends or reinforcement may sometimes meet the requirement more efficiently.

6. Indoor or Outdoor Use

Thickness is not the only consideration for outdoor sheet metal.

Exposure to moisture, salt, chemicals and changing weather conditions can affect the material. Depending on the environment, buyers may need to consider:

• Galvanised steel

• Suitable painted or coated steel

• Stainless steel

• Aluminium

• Protective coatings

• Correct drainage and installation

• Ongoing maintenance

A thicker untreated sheet is not necessarily more suitable outdoors than a correctly selected and protected material.

Is 1.6 mm Steel Suitable for Fabrication?

Yes, 1.6 mm steel can be suitable for many general fabrication applications, but its suitability depends on the design.

It may be considered for:

• Brackets

• Cabinets

• Trays

• Guards

• Panels

• Light frames

• Fabricated workshop components

However, 1.6 mm steel should not automatically be selected for every project. A wide unsupported panel may flex, while a smaller folded component may be relatively rigid.

Before choosing it, consider:

• Component dimensions

• Steel grade

• Load

• Number of bends

• Welding process

• Impact exposure

• Required finish

• Support spacing

For a structural, load-bearing or safety-critical application, the specification should be confirmed by a qualified engineer or fabricator.

What Thickness Sheet Metal Is Best for Outdoor Use?

There is no universal best thickness for outdoor applications because durability depends on more than the amount of metal.

The most appropriate material should be selected according to:

• Location

• Rain and moisture exposure

• Coastal salt exposure

• Chemical exposure

• Expected service life

• Protective finish

• Maintenance

• Structural requirements

For example, galvanised or appropriately coated steel may be considered where additional corrosion protection is required. Aluminium may be considered when lower weight and natural corrosion resistance are important. Stainless steel may be specified for certain demanding or hygienic environments.

The correct decision combines material type, grade, thickness, finish and installation design.

How Aluminium Sheet Thickness Differs From Steel

Aluminium and steel should not be compared using thickness alone.

Aluminium is lighter than steel, but different alloys and tempers offer different levels of strength and formability. A steel component and an aluminium component designed for the same purpose may therefore require different thicknesses.

When choosing aluminium sheet thickness, consider:

• Alloy

• Temper

• Strength requirement

• Component size

• bend requirements

• Welding

• Surface finish

• Corrosion environment

• Weight target

Do not use a mild steel gauge conversion to order aluminium. Always confirm the aluminium thickness in millimetres and specify the required alloy and temper where known.

Information to Provide When Requesting a Quote

A clear enquiry helps a supplier recommend available options and prepare more accurate pricing.

Include:

• Material type

• Grade or alloy, if known

• Thickness in millimetres

• Sheet width and length

• Quantity

• Finish or coating

• Cutting requirements

• Delivery suburb and postcode

• Required date

• Drawings or specifications

When the required thickness is uncertain, explain the application rather than guessing. Include the component size, expected load, environment and fabrication process.

Common Steel Sheet Selection Mistakes

Selecting by Price Alone

The lowest-cost sheet may not provide the required strength, grade, finish or durability.

Assuming Thicker Is Always Better

Unnecessary thickness increases cost and weight and can make cutting, bending and handling more difficult.

Using the Wrong Gauge Conversion

A gauge number must be matched to the correct material. Steel, stainless steel and aluminium gauge values are not interchangeable.

Ignoring the Grade

Thickness does not replace the need to select an appropriate steel grade.

Forgetting Fabrication Requirements

The sheet must work with the intended cutting, forming, welding and finishing processes.

Ignoring Corrosion Exposure

Outdoor and industrial environments may require a different material or protective coating.

Final Recommendation

The best steel sheet thickness is the one that meets the project’s strength, fabrication, weight, durability and budget requirements without unnecessary material.

Use millimetres as the main measurement wherever possible. When a drawing uses gauge, convert it using the correct sheet metal thickness chart for that specific material and confirm the result before ordering.

For straightforward components, a fabricator or experienced supplier may help identify suitable product options. Structural, load-bearing, regulated and safety-critical applications should be reviewed by an appropriately qualified professional.

To request pricing, provide The Steel Market Victoria with the material, thickness, dimensions, quantity, finish and delivery location. Our team can review the enquiry and confirm available steel and aluminium products for retail, trade and industrial requirements.