Sheet metal gauge is defined as a number for measuring how thick a sheet of metal is. You need to know it for your work with metal.
The most basic rule is: greater gauge numbers represent thinner metal. This is the opposite of what one might think. A perfect example is that 22 gauge steel is way thinner and bends easier than 16 gauge steel.
Another confusing point is this: gauge numbers mean different thicknesses for different metals. A 16 gauge piece of steel is not the same thickness as 16 gauge aluminum.
This document will make you a pro with sheet metal gauge. By the end, you will be a master of the system. The following subjects will be treated:
- The concept of gauge and its invert working logic.
- A detailed chart for the conversion of gauge to inches and millimeters.
- Tips on how to choose the right gauge for the project.
- Ways to measure sheet metal thickness yourself.
The Basic Rule: Understanding the “Why” Behind Sheet Metal Gauge
To fully appreciate what gauge is sheet metal, we have to look into its history. The system seems strange, but there is a simple reason for its design. It is a means of communicating the amount of metal thickness effectively.
The Inverse Relationship: Higher Gauge = Thinner Metal
As we said before: the higher the gauge number, the thinner the metal. This practice derives from the wire production industry.
In earlier days, workers made wire thinner by pulling it through a device called a die. The gauge number was the one to inform you how many times the wire moved through the die. For instance, a wire drawn 20 times (20 gauge) would be thinner than a wire drawn only 10 times (10 gauge). This was the very same idea that was applied to sheet metal.
Turning Sheet to Plate: When is Gauge Finished?
The gauge system is used for thinner materials. Once metals reach a certain thickness, we stop using gauge numbers and use the term “plate” instead.
The rule of thumb is any metal that is thicker than 7 gauge is referred to as a plate. This is close to a thickness of around 3/16 of an inch or 4.5mm. For metal plates, we simply put the thickness in inches or millimeters like “1/4 inch plate”. Thus, it becomes way more straightforward to discuss thick materials. As noted in this guide to Understanding Sheet Metal Types, Gauges and Thicknesses, the industry uses decimal or fractional inch callouts for these heavier materials.
Why 16 Gauge Steel is NOT the Same as 16 Gauge Aluminum
Here is the biggest source of mistakes for new learners. It is essential for you to realize that a gauge number means different thicknesses for different metals. If you end up ordering the wrong one, your work may fail.
Knowing the difference between various sheet metal gauge systems is imperative for acquiring the right material. This is critical when deciding what gauge is sheet metal for a job.
The Great Divide: Iron and Non-Iron Metals
The main reason for this difference is density, or how much the metal weighs. Gauge systems were first based on the weight of the metal per square foot.
Steel is a ferrous metal, which means it contains iron. Aluminum, in contrast, is a non-ferrous metal. The main point is that steel is much heavier than aluminum. Therefore, a steel sheet and an aluminum sheet of the same thickness will be totally different in terms of weight.
The Manufacturers’ Standard Gauge for Sheet Steel is based on 41.82 pounds per square foot for a one-inch-thick sheet. Other metals have different weights, so they need their own gauge scales.
The Systems You’ll See the Most
To avoid mistakes, you must know which system to use for your metal. Using the right chart is key. The leading systems are:
- Manufacturers’ Standard Gauge (MSG): It is the most popular one to use. We use this system for standard, galvanized, and stainless steel.
- American Wire Gauge (AWG): Sometimes called the Brown & Sharpe Gage. It is used for non-ferrous metals, like aluminum, brass, and copper.
- Birmingham Gage (BG): Although less used today, you may still find it in some types of metal strips and tubing.
As noted, knowing what gauge is sheet metal also means knowing what kind of metal you work with. To get more details, check out this A Comprehensive Guide on Sheet Metal Gauge Charts.
The Best Sheet Metal Gauge Chart (Side-by-Side Comparison)
The most efficient way of determining the specific thickness of a sheet metal gauge is by using a chart. It completely erases the possibility of errors and uncertainties. This chart provides an overall view of the most commonly used materials side-by-side.
To use this chart, first find the specific type of metal you are using (for example, Standard Steel). After that, find your desired thickness in inches or millimeters. Look to the left to see the gauge number that matches it. Or, if you happen to know the gauge, find it in the first column and look across to find its actual thickness.
| Gauge No. | Standard Steel (in / mm) | Stainless Steel (in / mm) | Aluminum (AWG) (in / mm) |
|---|---|---|---|
| 7 | 0.1793″ / 4.55mm | 0.1875″ / 4.76mm | 0.1443″ / 3.67mm |
| 8 | 0.1644″ / 4.18mm | 0.1719″ / 4.37mm | 0.1285″ / 3.26mm |
| 9 | 0.1495″ / 3.80mm | 0.1563″ / 3.97mm | 0.1144″ / 2.91mm |
| 10 | 0.1345″ / 3.42mm | 0.1406″ / 3.57mm | 0.1019″ / 2.59mm |
| 11 | 0.1196″ / 3.04mm | 0.1250″ / 3.18mm | 0.0907″ / 2.30mm |
| 12 | 0.1046″ / 2.66mm | 0.1094″ / 2.78mm | 0.0808″ / 2.05mm |
| 13 | 0.0897″ / 2.28mm | 0.0938″ / 2.38mm | 0.0720″ / 1.83mm |
| 14 | 0.0747″ / 1.90mm | 0.0781″ / 1.98mm | 0.0641″ / 1.63mm |
| 15 | 0.0673″ / 1.71mm | 0.0703″ / 1.79mm | 0.0571″ / 1.45mm |
| 16 | 0.0598″ / 1.52mm | 0.0625″ / 1.59mm | 0.0508″ / 1.29mm |
| 17 | 0.0538″ / 1.37mm | 0.0563″ / 1.43mm | 0.0453″ / 1.15mm |
| 18 | 0.0478″ / 1.21mm | 0.0500″ / 1.27mm | 0.0403″ / 1.02mm |
| 19 | 0.0418″ / 1.06mm | 0.0438″ / 1.11mm | 0.0359″ / 0.91mm |
| 20 | 0.0359″ / 0.91mm | 0.0375″ / 0.95mm | 0.0320″ / 0.81mm |
| 21 | 0.0329″ / 0.84mm | 0.0344″ / 0.87mm | 0.0285″ / 0.72mm |
| 22 | 0.0299″ / 0.76mm | 0.0313″ / 0.79mm | 0.0253″ / 0.64mm |
| 23 | 0.0269″ / 0.68mm | 0.0281″ / 0.71mm | 0.0226″ / 0.57mm |
| 24 | 0.0239″ / 0.61mm | 0.0250″ / 0.64mm | 0.0201″ / 0.51mm |
| 26 | 0.0179″ / 0.45mm | 0.0188″ / 0.48mm | 0.0159″ / 0.40mm |
| 28 | 0.0149″ / 0.38mm | 0.0156″ / 0.40mm | 0.0126″ / 0.32mm |
Choosing the Right Gauge: A Practical Guide
Knowing the numbers is one thing, but picking the right material for your project is a different story. The following section serves as a practical guide for you in selecting the right sheet metal thickness for common jobs.
The right choice will affect strength, weight, cost, and the ease of working with the metal.
Car Body Panels & Repair
The gauge for car panels has evolved over the years. The correct decision depends on the car’s age and which part you are making.
- Classic Cars (before the 1970s): Old cars were built with thick steel. Body panels were mostly 18 or 19 gauge steel.
- Modern Cars: Newer cars use thinner, high-strength steel to save weight. Panels are often 20 to 22 gauge.
- Patch Panels: When you want to fix rust, 18 or 20 gauge steel will be a good choice. It is strong and easy to work with.
HVAC Ductwork
Heating and air conditioning duct metal must be light and cost-efficient. The gauge is selected based on whether it is for a house or a larger commercial building.
- Home Use: The most common type of ductwork in houses is 24, 26, or even 28 gauge galvanized steel. It is thin, light, and easy to install.
- Commercial Use: Ducts in commercial buildings require more air and are therefore stronger, often needing 20 or 22 gauge steel.
Roofing & Flashing
Metal roofing has a long life. The gauge used is an essential factor for the roof to resist damage from hail, wind, and other elements.
- Steel Roofing: A popular choice for home metal roofs is 24 or 26 gauge steel.
- Copper & Aluminum Flashing: This metal is used to seal joints on a roof. It is generally sold either by weight (like 16 oz copper) or by its direct thickness (like 0.032″ aluminum).
Brackets, Boxes, and General Building
For custom jobs, the correct thickness of metal is determined by the purpose of the part. What gauge is sheet metal for a simple bracket versus a heavy-duty frame?
- Light-duty brackets: For brackets that hold a small amount of weight, 16-18 gauge is often powerful enough.
- Sturdy boxes/cases: For electrical boxes or machine guards, 12-14 gauge provides good strength and protection.
- Heavy structural parts: For frames or supports that bear a lot of weight, 10 gauge or thicker is the only way to go. You are now heading into “plate” territory.
Getting expert help is advisable for complicated projects. Collaborating with specialists in fabrication de tôles ensures the right material and gauge are chosen for the best performance and price.
How to Measure Sheet Metal Gauge in the Real World
Sometimes you have a sheet of metal and want to know its thickness, but you can’t just guess. Here is how we determine the thickness of sheet metal correctly in the shop.
The gauge of any sheet can be found quickly and accurately if the right tool and technique are used.
The Right Tools for the Job
You have different measuring options. Each one offers a different balance of speed and accuracy.
- Sheet Metal Gauge Tool (Wheel Gauge): This is the classic, quick-and-easy tool. It is a flat metal disc with gaps of different sizes around the edge. You insert the metal piece into the gaps until you find one that fits perfectly. The number next to that slot is the gauge. It’s quick, but it isn’t as detailed as other tools.
- Digital/Dial Calipers: This is our preferred method for precise work. Calipers give you an accurate decimal reading in either inches or millimeters. You then check that number against a gauge chart to find the gauge.
- Micrometer: A micrometer is the correct tool for the highest level of accuracy. However, it is typically more precision than is required for general sheet metal work.
A Step-by-Step Guide to Measuring with Calipers
Using digital calipers is a breezy and reliable way. You can follow these steps to get a perfect measurement every time.
- Clean the Edge: First, make sure that the edge of the metal is clean. Any dirt, paint, or rough edges can make your reading wrong.
- Zero the Caliper: Switch on the caliper and completely close its jaws. Press the “ZERO” button to set it to zero.
- Measure Carefully: Open the jaws and place them onto the sheet metal. Close them gently. Do not clamp down hard. Squeezing too tightly can bend thin metal and give you a false, smaller reading.
- Take Multiple Readings: Measure the thickness in a few different places along the edge to check that the whole sheet is of the same thickness.
- Check Your Chart: Take your decimal reading (for instance, 0.0478 inches) and locate it on a gauge chart. Verify that you are using the correct column for the metal type (steel, aluminum, etc.) to find the right gauge number.
Conclusion: From Confusion to Clarity
Understanding what gauge is sheet metal doesn’t have to be a difficult task. The moment you learn the basic rules, the system becomes a powerful resource for any builder, engineer, or DIYer.
Let’s summarize the three major points. First, a higher gauge number always means a thinner piece of metal. Second, gauge standards are different for different metals, like steel and aluminum. Third, you must always use a chart for converting a gauge number into an accurate measurement in inches or millimeters.
Armed with this guide, you now possess the know-how to confidently discuss, select, and check sheet metal. This skill is a foundation for any project. For projects that require precision beyond sheet metal, such as turned parts, understanding material properties is just as important. Our expertise at Mékalite spans the full manufacturing spectrum, including advanced Services de tournage CNC for the most demanding applications.
Common Questions (FAQ) about Sheet Metal Gauge
Is 16 or 18 gauge sheet metal thicker?
16 gauge sheet metal is thicker. Always remember the backward rule: the lower the gauge number, the thicker the metal. For example, 16 gauge standard steel is about 1.52mm thick, while 18 gauge steel is only about 1.21mm thick.
What gauge sheet metal is used for car frames?
Car frames and unibody structures are very complex. They use many types of high-strength steel and are not usually described with simple gauge numbers. These parts are engineered with thicknesses that can range from 1.5mm to over 3mm. This is roughly equal to 16 gauge down to 11 gauge, but the specific strength of the steel is more important than the gauge alone.
Can I use a steel gauge chart for aluminum?
No, you should never use a steel chart for aluminum. Steel and aluminum use different gauge systems. The MSG system is for steel, while the AWG system is for aluminum. For instance, 18 gauge steel is 0.0478 inches thick, but 18 gauge aluminum is 0.0403 inches thick. Always use a chart made for the specific metal you are measuring.
What is the thinnest sheet metal gauge available?
Sheet metal can be made very thin. Some specialized uses have gauges as high as 38 gauge, which for steel is only 0.0060 inches thick. However, for most general projects, 28 or 30 gauge is the thinnest you are likely to find and use.
Does paint or coating affect gauge measurement?
Yes, it absolutely does. A thick layer of paint, powder coat, or a galvanized zinc coating adds to the total thickness. If you measure a coated surface, you will get a wrong reading. For an accurate measurement of the metal itself, you must always measure on a clean, bare edge.
