Complete Guide to Sheet Metal Thickness, Gauge and Tolerances

In metal fabrication, understanding various sheet metal data is very important. From sheet metal thickness to gauge, and then to manufacturing tolerances, each data must be quite precise. Otherwise, even a perfect sheet metal enclosure could suffer bending or cracking due to incorrect material thickness. It can be said that these data determine the weight, structural strength, manufacturing cost of the product, and even limit the machining technology you can use. Therefore, for those involved in sheet metal fabrication, this guide article is a must-read.

What is Sheet Metal Thickness?

Working in the shop, you must be familiar with the phrase ‘sheet metal thickness’. In fact, it is the physical dimension of the sheet metal in the direction perpendicular to its surface. And we commonly use millimeters (mm) or decimal inch(inch) as the unit to describe sheet metal thickness.

Why is Sheet Metal Thickness So Important?

Sheet metal thickness can determine whether a project succeeds or fails sometimes. There are mainly the following situations:

Strength and Weight: The most intuitive physical attribute. The thicker the sheet is, the more rigid it is.

Manufacturing Limits: Thicker sheets are difficult to process, and the bending force required by the bending machine will increase. You also need to design a larger minimum bend radius to prevent the metal from cracking under force.

Welding: If the sheet is too thin, it is easily burned through during welding.

Assembly: If the sheet is too thick, it can also cause assembly problems with structural parts or plug-in parts.

How to Measure Sheet Metal Thickness?

After explaining sheet metal thickness, let’s discuss how to measure the sheet metal thickness. In our real manufacturing shop or inspection (IQC) process, measuring sheet metal thickness is an operation that requires experience and tools. Any wrong measurement can lead to serious tolerance issues.

1. Calipers

This can be considered the most common and convenient tool. Its accuracy can usually reach ±0.02mm (0.001″). When measuring, you need to avoid burrs on the edges, and also pay attention to the strength of the measurement to prevent the material from deforming.

2. Micrometers

When you need to measure very thin sheet metal, or need to check to see if the manufacturing tolerances of the material meet standards, then a micrometer is a better choice. Micrometers typically achieve accuracy around ±0.001mm (0.00005″).

During use, you should pay attention to using the ratchet stop. This is especially important when measuring sheets with soft coatings.

3. Wire Gauge

This is a round or rectangular metal plate with many notches of different widths, each marked with a corresponding gauge number and decimal thickness. You can use it if you need to quickly confirm material specifications on site.

And the operation is very simple. You just need to slide the edge of the sheet metal into the notch of the gauge. However, one thing you should note is that non-ferrous metals (such as aluminum, copper) and ferrous metals (such as steel) use different gauge standards.

Additionally, in your actual measurements, you should also pay attention to the impact of surface treatment.

• Galvanized Steel: The thickness you measure includes the substrate (steel) and the zinc layer on both sides.
• Powder Coating: If you are measuring a finished part that has already been powder coated, you must also subtract the coating thickness to obtain the true substrate thickness

Choosing the Right Sheet Metal Thickness

In sheet metal design, you only need to consider the following two points when choosing the appropriate thickness.

1. Structural Rigidity

This is the most intuitive requirement. If the sheet metal is large and the material is too thin, the sheet metal surface is prone to oil-canning, thereby losing structural stability. At the same time, you cannot blindly increase the thickness, which will increase the weight of the final product. Therefore, my suggestion is that you can increase strength through geometric design, such as adding flanges, ribs, or hems, etc.

2. Cost

Cost is obviously also a factor that you must consider. Increase the thickness of the plate, and the cost will also increase. I suggest that you always design based on the supplier’s standard stock specifications. If you insist on ordering sheets of a specific thickness, you will have to accept a very high minimum order quantity (MOQ), and the project may be delayed.

What is Sheet Metal Gauge?

Gauge is a commonly used term used to refer to metal thickness. Especially in North America, engineers and purchasing personnel use gauge to denote metal thickness. For example, for a 1.5mm steel plate, North American engineers would say “16 Gauge steel plate”.

How Sheet Metal Gauge Works?

Gauge (usually abbreviated as Ga. or G) is not an absolute unit of physical measurement. It is an industry standard code representing material thickness. Different metals may have the same thickness, but they have different gauge.

Also, you need to remember this golden rule about gauge: the higher the gauge number, the thinner the metal. And vice versa.

Why Do Sheet Metal Gauges Matter?

For the manufacturing industry, the reason why gauge is so important is mainly due to the following reasons.

1. The Language of Supply Chain

In reality, many steel and aluminum mills conduct large-scale rolling and shipping according to standard gauge specifications. In North American processing plants, workers also communicate with one another using gauge as a reference.

2. Tooling and Process Parameters

The choice of gauge directly determines the physical machining process of the sheet metal part, and the operator will choose the corresponding mold based on the gauge on your drawing. And the parameters of the machine tool are also preset around the standard specification.

3. Cost Estimation

You should know that the weight conversion of gauge is still one of the quick cost calculation methods in the industry.

Sheet Metal Gauge Thickness Chart

Different materials follow completely different specification standards. Below, I will provide you with the sheet metal gauge thickness chart used by DSR company.

Steel Gauge Chart

The most commonly specified base materials on your sheet metal drawings will typically be cold-rolled steel or hot-rolled steel. Both materials use the same thickness specification (MSG standard), but have different costs, appearances and uses.

HRS vs. CRS

Hot-rolled steel (HRS) is formed by rolling at extremely high temperatures (over 1700°F). After cooling, its surface forms a rough, bluish-gray scale. This steel is cost-effective and is usually used for heavy-duty structural parts, industrial bases, etc. that do not require high surface finish.

And cold-rolled steel is hot-rolled steel that has undergone further pickling and cold rolling at room temperature. After this process, the oxide scale is removed from the steel’s surface, leaving it extremely smooth. At the same time, the yield strength and dimensional accuracy of the steel will be significantly improved. However, cold-rolled steel is slightly more expensive and is suitable for all consumer electronics casings, precision chassis, etc.

Steel Sheet Thickness Chart

Industry Standards:

Standard Steel/Carbon Steel: Based on Manufacturer’s Standard Gauge (MSG).

Galvanized Steel: Also based on the MSG standard, but you will find that its values are always slightly thicker than standard steel. This is because it includes the thickness of the double-sided hot-dip galvanized layer.

Stainless Steel: Based on United States Standard Gauge (USG).

Aluminum Gauge Chart

Aluminum alloys are based on the american wire gauge (AWG), also known as the brown & sharpe gauge. This system is also specifically used for non-ferrous metals, including aluminum, brass, and copper. The core reason for using this standard is the huge difference in material density

Aluminum Thickness Chart

Other Metals Gauge Chart

Below are some other material gauge charts from DSR company.

Copper & Brass Gauge Chart

Copper and brass follow the AWG (American Wire Gauge) system exactly.

Zinc Gauge Chart

Zinc sheets use a proprietary zinc gauge system. Its logic is that the larger the gauge value, the thicker the material.

 Pro Tip for Engineers:

Don’t just mark the gauge number on the manufacturing drawings. Be sure to indicate the decimal thickness along with the material type. This can help you eliminate a lot of communication ambiguity.

* Of course, if you need to download these charts, here we provide you with a comprehensive PDF file, hoping it will be helpful to you: DSR Comprehensive Sheet Metal Gauge Charts.pdf.

DSR Gauge to Thickness Conversion Gadget

If you want to quickly query the results, you can also use this tool we provide, which is very simple and practical.

What is Sheet Metal Tolerance?

Similar to the CNC machining tolerances we discussed before, sheet metal Tolerance is also the maximum reasonable range that allows the actual dimensions of a part to deviate from the ideal design value. However, sheet metal fabrication involves cutting, stretching, metal bending, and welding thin metal sheets, and these processes are more likely to cause stress deformation and thermal contraction of the material, thereby affecting the final dimensional accuracy.

Sheet Metal Tolerance Types

• Cutting& Blanking tolerance: The accuracy of the outline profile and aperture size is extremely high.
• Bending & Forming tolerance: The more times you bend, the more serious the tolerance stack-up will be.
• Welding & Assembly tolerance: Welding fuses multiple parts together and the extremely high heat input can cause severe warping and shrinkage.

Sheet Metal Tolerance Standards

The tolerance standards for sheet metal are mainly these three: ASTM A568, ASTM A480, EN 10130 / 10131. And I will show you their distinction in detail in a table.

Sheet Metal Fabrication Tolerance Chart

Different machining equipment and processes determine the tolerance limits for different features of the part.

Practical Tips for Sheet Metal Fabrication

Finally, regarding your sheet metal design, I would like to offer some personal practical suggestions.

Design Guidelines for Sheet Metal

1. Minimum Bend Radius

The inside radius of most materials should be at least equal to the thickness of the sheet (R≥1t). For harder materials, this factor may even need to be increased to 2t or 3t.

2. Hole-to-Edge Distance

The distance from the edge of a hole to the bend line should be at least 3 times the thickness of your sheet plus the inside bend radius (3t+R).

3. Flange Depth Limits

The minimum inside height of a flange is typically required to be greater than 4 times the sheet thickness (4t).

4. Forming & Dimple Depth Limits

The forming depth should not exceed 2 to 3 times the thickness of the sheet, otherwise it is very easy to cause the material to thin or even crack.

Tolerances in Bending and Forming

Bending is a dynamic process full of variables.

1. Angle tolerance

In sheet metal fabrication, it is difficult to achieve absolute precision in bending angles. For a standard CNC bending machine, ±1° is a very reasonable tolerance expectation, while if the bending edge is very long, the tolerance may need to be relaxed to ±2°.

2. Dimensional Tolerance

±0.13mm: This represents the maximum precision achievable in a single bend under ideal conditions, and requires extremely high-quality sheet metal and precision dies.

±0.25mm: This is the most common and cost-effective standard linear bending tolerance in the workshop. However, after multiple bends, this error will accumulate progressively.

3. Springback Compensation

All metal springs back, so manufacturers use sharper-angled dies for over-bending. As a designer, you don’t need to draw springback in the 3D model, but you must leave enough assembly clearance when designing the internal structure.

Common Mistakes to Avoid

• Ignoring the gauge differences of different materials
• Overly tight tolerances lead to skyrocketing costs
• Does not account for material thickness variations
• You didn’t follow the minimum bend radius guidelines in your design
• Mixing Gauge and Millimeters can lead to confusing work

Conclusion

That’s all. I believe this article will be helpful to your design and manufacturing. However, when it comes to the manufacturing phase, in addition to data, you also need a trustworthy partner. Our DSR company can provide you with tailor-made CNC machining and sheet metal fabrication services. Our engineers will also work closely with you to optimize your designs and select the most suitable materials. At the same time, we ensure perfect delivery from cutting and forming to final surface treatment.

FAQ 

Q1: What is the ISO tolerance standard for sheet metal?

A: In the field of sheet metal fabrication, the most widely used general tolerance standard is ISO 2768, which is mainly used for linear dimensions and angular dimensions without specified tolerances.

Q2: How is thickness specified for sheet metal?

 A: Gauge and actual physical dimensions.

Q3: What is the thickness tolerance of ASTM A1011?

 A: ASTM A1011 is the standard specification for hot-rolled carbon steel sheet. The thickness tolerance is not a fixed value, but varies based on the nominal thickness of the material and the width of the steel sheet.

Q4: What are the 4 types of tolerance?

 A: Limit tolerance, bilateral tolerances, unilateral tolerances and GD&T.

Q5: What is 6H and 6g tolerance?

 A: In precision machining, 6H and 6g are the most common standard tolerance class fits for ISO metric threads.

The number ‘6’ represents a medium accuracy grade. The capital letter ‘H’ specifically refers to internal threads, which have a zero basic tolerance. The lowercase letter ‘g’ specifically refers to external threads, which have a small negative deviation.

Q6: What is the most common style of thickness gauge?

 A: Circular wire and sheet metal gauge.

Q7: What is the standard gauge for 1/8 inch steel plate?

A: In the standard carbon steel gauge system, the closest thickness to 1/8 inch is 11 gauge. Its standard thickness is about 0.1196 inches (about 3.04 mm).

Q8: Custom fabrication services for 20 gauge stainless steel?

 A: Fiber laser cutting, CNC stamping and precision bending.

Q9: What is 16 gauge steel used for?

 A: 16 Ga steel sheets are widely used in the manufacture of industrial aluminum enclosures, heavy-duty HVAC ducts, metal tool boxes, automotive exhaust ducts, and various types of metal cabinets.

Q10: What is stronger, 14 or 16 gauge steel?

 A: 14 gauge steel sheet is thicker than 16 gauge, therefore 14 gauge steel sheet is also stronger.

Q11: Is 18 or 20-gauge steel better?

 A: 18 gauge (about 1.2 mm thick) is thicker and stronger than the 20 gauge (about 0.9 mm thick).

Q12: What are the sizes of sheet metal?

 A: When evaluating sheet metal dimensions, engineers typically standardize definitions based on two dimensions: thickness (gauge/mm) and planar width and length (width×length).

Q13: How thick is car sheet metal?

 A: 20 to 22 gauge steel or aluminum alloys.

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