This is a metal supply house. You walk down the aisle and see sheet after sheet of aluminum stacked on shelves. If you don’t know what to look at they all look the same. Gauge numbers printed on sheets. But you can’t interpret those numbers until you know what they mean.
That’s the first trap. The second trap? Assuming aluminum act like steel. It doesn’t. If you pick the wrong thickness you waste your time and money, and chances are you’ll find yourself back at the store again.
How to Choose the Right Aluminum Sheet
The gauge numbers represent the Brown and Sharpe system for measuring the thickness of sheet metal. It’s the industry standard used for all non-ferrous metals. Gauge numbers increase as thickness decreases. This goes against everything new fabricators expects to see, so it’s easy to make a mistake. A larger number represents a thinner sheet. It sounds backwards, but it makes sense once you get used to it.
Small details matter, especially if you’re buying material for boat hull or a roof. From left to right on the chart, you can track from thick plate up through thin foil. The thickness bars is getting smaller as they go from gauge three up to gauge thirty. That’s what makes it easy to grasp just how substantial gauge sixteen is. Gauge twenty-four seems close to heavy card stock. And most of your applications will be somewhere in the middle range.
Gauge fourteen to eighteen is typically what you want for gutters, siding, light framing. That’s the sweet spot for fabrication. You have enough stiffness to work the metal, but you don’t need an industrial press to bend it into shape. For something like a trailer frame, you’re looking at gauge eight or ten. You want something that has a little bit more structure for holding up out on road so you’ll pick heavier material.
That is only half the story. Half of it is thickness. Alloy is equally important. The infographic highlights four families of alloys: 1100, 3003, 5052 and 6061. You can’t select a gauge and stop there. Select the type of metal based off what that part is going to be exposed to.
The 3003 family is the workhorse of general fabrication. It makes a good countertop material. It resists corrosion decently and it forms well. It is great for HVAC ducts. But if it’s salt water you’re looking at, then it needs the 5052 alloy. It has a higher amount of magnesium, giving it better marine resistance. Many times people will get cheap aluminum in an effort to fix their boats and they make mistakes.
Then you have 6061 alloy, which is another different animal altogether. It is strong and heat-treatable. It is good for bicycle parts and structural frames, but it doesn’t form well. You’ll have to anneal it first, otherwise you run the chance of cracking it when bending.
Weight is another practical consideration. At an equal thickness, aluminum is approximately one-third of the weight of steel. To determine approximate weight per square foot, there’s a formula on the chart. That will allow you to estimate load limit or shipping cost. Using our quick example above, we find a gauge sixteen sheet has a weight of approximately 0.7 lbs/square foot. Being lightweight is good but you need a heavier gauge to get the same rigidity.
So no, don’t use a steel gauge chart with aluminum. It just doesn’t work the same. Gauge sixteen steel is thicker than gauge sixteen aluminum. Eliminate all of that confusion completely when you order by decimal inches. Always spec out exact thickness on your purchase order.
When cutting material, measure first then cut. The thickness of your sheet will vary slightly based off mill tolerance. Due to mill tolerances, your gauge sixteen sheet might actualy be slightly thicker or thinner than listed. Using a micrometer takes thirty seconds. Save yourself hours of frustration down the road.
Thin Stock (<18 gauge) is difficult to weld. Keep heat under control to prevent burn thru. Often riveting or bonding with adhesives is wiser. This applies to very thin material. Chart comparison shows how much material is saved by just stepping up two gauge sizes. That’s a huge saving in cost and weight.
3003 is corrosion resistant and easy to bend but less strong, while 6061 is strong but doesn’t form easily. 6061 is strong, but it doesn’t form as easily. Strong means heavy duty, but it is heavier.
There’s no such thing as “the perfect” gauge. Just like there are many other things in life, there is simply the right gauge for each task at hand. What is the first step? Start with the application. What are its requirements? Then review the thickness and make sure you actualy have the right gauge.
And that transforms a confusing variety of sheet metal into a useful collection of tools. You leave the hardware store knowing exactly what you’ve got. It is not what you thought you might get, but exactly what you need.
