Understanding Steel Thickness Charts and Conversions

There are numerous standards and conventions when it comes to steel thickness; different countries call it different things and use different units to measure it. This, coupled with the centuries of evolving technologies, makes something that should be relatively easy to figure out quite complex.

In this guide, we’ll answer some of the most common questions on steel thicknesses, including how they vary by material type and how to convert them.

What Are Gauge Sizes? Steel Thickness Explained

The gauge of steel sheet is simply a standardized system of thickness measurement. Similar to how electrical wire is measured, the higher the gauge number, the thinner the sheet thickness.

For a list of mild steel thickness gauges, our full guide here shows various charts.

Gauge vs Inches vs Millimeters

The unit of measurement a metal is measured in is likely to depend on what type of metal it is and where you are in the world.

• Sheet metal Gauge: Gauge is commonly used to measure sheets up to 7 gauge/4.5 mm. Gauge is commonly used in North America and in traditional blueprints in other parts of the world. It can be used on various types of metal, including mild steel, stainless steel, and aluminum
• Inches: the most commonly used unit in North America, and still used in Europe for non-ferrous materials such as aluminium and copper
• Millimeters: Used across the world for a range of metal types, sheet thicknesses designated in millimeters are often still derived from their imperial equivalents

Why Gauge Sizes Vary by Material Type

It’s said that sheet metal gauges were originally coined by weight, and therefore, the metal’s density affects the actual thickness of each material, particularly between two materials of largely different densities.

For instance, 8-gauge aluminum is 3.2mm thick, whereas 8-gauge stainless steel is 4.365mm thick.

Converting Gauge Sizes for Fabrication Accuracy

When working with sheet metal measured in gauge rather than millimeters or inches, it can sometimes be helpful to convert these when manufacturing.

One example of when this can be useful is when calculating flat lengths for folding, where a ratio of the thickness, accounting for the type of tooling, is added to the bent dimensions.

One of the easiest ways to do this is to keep a reference book or chart of common material gauges to hand, allowing quick conversions.

It is important to remember that gauges vary in thickness depending on the type of metal, as discussed above. So if a part is made from 8-gauge mild steel and then in 8-gauge aluminum, the various bend lengths, etc., will need to be recalculated.

Tips for Selecting the Right Thickness

The thickness of metal used in a project can determine its strength, ability to be manufactured, and weight.

While simply increasing the thickness can make a part stronger, if any complex bends or forming is needed, this may be difficult in much thicker materials. Similarly, using a metal that is too thin for the purposes of manufacturing can make the part too weak to support the stresses involved.

Another consideration is cost; the thicker the metal, the more weight and volume are present, meaning a higher cost to buy, which can quickly add up with a large part or high quantity.

Calculating sheet metal part strength

Many software packages allow for FEA (finite element analysis) on designed components, allowing you to visualize the likely stresses in the part and whether the material can withstand them.

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