MIG Wire Sizes: How to Choose the Right Size for Your Projects

Table of Contents > 1. About MIG Welding Wires     1.1 MIG Wire Composition     1.2 MIG Wire Sizes 2. How to Choose the Right MIG Wire Size for Your Applications     2.1 Wire Size Based on Thickness of the Metal         2.1.1 MIG Welding Wire Size Chart     2.2 MIG Wire Diameter and Penetration     2.3 MIG Wire Sizes and Deposition     2.4 MIG Wire Size and Welding Position     2.5 Joint Configuration and Wire Sizes     2.6 Wire Size and Weld Quality     2.7 MIG Wire Size and Welder Limitations 3. What Happens When You Choose a MIG Wire That Is Too Large for Your Application? 4. What Happens If You Use a MIG Wire That Is Too Small for Your Applications? 5. Quick Tips on How to Choose the Right MIG Wire Size     5.1 Bonus Tips When Choosing the MIG Wire 6. 🧐MIG Wire Sizes: How to Choose the Right Size for Your Projects FAQ

MIG wire is a central part of MIG welding. It serves as both an electrode that transfers the heat and a filler metal that fills the joint and fuses with the pieces.

To achieve the highest-quality results in your welding project, you will need the correct MIG wire. MIG wires vary in composition and size, and matching these properties to the type of metal, thickness, joint configuration, and desired penetration is crucial in producing sound welds.

In this article, we will focus on MIG wire sizes and answer the common question of how to choose the right size for your projects and get the best results.

 MIG Welding Process
Source: https://www.youtube.com/watch?v=BsLbCEChpe0

About MIG Welding Wires

MIG welding wire is a consumable and an essential part of MIG welding. It comes in spools, ranging from 2-10 lbs for hobby applications to 20 lbs and more for industrial applications. You mount the wire spools inside the wiring compartment of your MIG welder.

The wire feeding mechanism automatically feeds the wire from the spool over the drive rolls into the liner and MIG gun. As it feeds, the MIG wire serves as an electrode that transfers the heat and melts the base pieces. Simultaneously, wire is a filler metal that fills the joint and fuses with the parent metal.

As a result, you cannot weld without a MIG wire. Fundamentally, MIG wires vary in composition and wire diameter.

Different Types of MIG Welding Wires
Source: https://onetouchexim.com/types-of-mig-welding-wire/

MIG Wire Composition

MIG wires are typically made of steel or aluminum, and they can have a copper coating.  The American Welding Society (AWS) classifies wires with a set of numbers and letters. Each letter and number in its nomenclature signifies a specific feature. The final goal is to match the composition of the wire to the base metal you are welding.

As a beginner or home welder, you should know there are different wire types for various metals. For example, if you are welding mild steel, you should use steel MIG wire, such as ER70S-6 or any in the ER70S classification. For aluminum, you will likely use ER4043 or ER5356 wires, and for stainless steel, it is usually ER308/308L.

Don't confuse MIG for Flux-cored wires. Although fundamentally similar, MIG wires are solid and unshielded. You must use external shielding gas to protect the MIG wire and weld from atmospheric contamination. Flux-cored wires are hollow and filled with flux. As it melts, the flux rises to the top and creates a protective layer that shields the weld from contamination. Flux-cored wires are FCAW-only, although you can use them with the same power source, the MIG/Flux-cored welder.

Cross-Section Views of Solid Wire and Flux-cored Wire
Source: https://materialwelding.com/metal-cored-welding-vs-flux-cored/

MIG Wire Sizes

The most common wire sizes for hobby and home applications and general metal fabrication are .024", .030", and .035". These sizes will cover most MIG welding and metal sizes up to 3/16" in a single pass.

DIY MIG Welding Metal Bender
Source: https://www.youtube.com/watch?v=ktFaQuDj3c4

In some industrial applications, the sizes can reach .040 or .045". However, these are designed for high-end applications over 300 amps and usually come in spools larger than 10, 30, or 40 lbs.

On the other hand, your typical home MIG welders, such as YesWelder DP200, will work best with .030"-.035” wires and spools up to 10 lbs. Using larger spools reduces downtime, but it can make the welder exceptionally heavy, so we don’t recommend it for your home applications.

Firstess DP200 Multi-Process DualPulse™ MIG Welder

How to Choose the Right MIG Wire Size for Your Applications

The diameter of the welding wire can significantly influence the quality of the weld, including strength, uniformity, and overall weld deposition. Therefore, choosing the correct diameter is key to producing sound welds.

MIG Welding Process
Photo by @thatshitsfireee (TikTok)

There are several factors to consider when choosing the MIG wire size for your applications. Most importantly, you should consider the following:

• Thickness of the material

• Weld penetration and deposition

• Joint configuration and welding position

• Quality of the welding process

• Welding machine recommendations

• Size of your welding gun

 

Wire Size Based on the Thickness of the Metal

The thickness of the metal is the most crucial factor when choosing the MIG wire diameter. The key is to select a wire that is large enough for the given material thickness. Here are some common recommendations:

• .024" wire: This wire is ideal for thin sheet metal, including thin parts of mild steel, aluminum, or stainless steel. Welders use it to MIG weld 24-18 ga metals, including thin exhausts, autobody panels, and light-duty materials. A .024" wire can provide precision even on thicker pieces, but it can yield a lack of penetration.

• .030" wire is the most popular wire diameter among hobbyists, DIYers, and home MIG welders. Its versatility makes it ideal for metals of 20 ga up to 1/8", which are the typical thicknesses you are likely to MIG weld in your home applications. This diameter is also the most used for a wide variety of applications, including construction work, shaft buildup, tanks, truck bodies, and general shop applications.

• .035" wire: You can use the .035" wire when welding the upper range of MIG welding thickness. The wire works with metals up to 3/8", including structural steel, general fabrication, and farm equipment repair. Keep in mind that you can also use it when welding thin pieces down to 16 ga to improve weld deposition. In some cases, you can use 0.040" wire to weld up to 1/2". However, MIG welding metals over 1/16" with lower-rated MIG welders is impossible without a multi-pass operation.

Flux-Cored Welding Using E71T-GS .035” Wire
Photo by @jrslawnmowingservice (TikTok)

MIG Welding Wire Size Chart

Data by Bakergas (https://bakersgas.com/pages/recommended-welding-wire-size-chart)

MIG Wire Diameter and Penetration

The size of the MIG wire can also dictate its penetration inside the weld joint, and the electrode part of the MIG wire can affect the heat input into the weld joint.

As an electrode, the wire transfers energy into the joint. Large wires can transfer more energy into the joint without evaporating and spatting around the workpiece. The heat is high enough to melt and penetrate the thicker base metal, producing sound welds, good penetration, fusion, and high depositions.

MIG Welding Thick Steel
Source: https://www.youtube.com/watch?v=sIgchLDoz9A

Meanwhile, small-diameter MIG wires transfer a limited amount of heat, which is necessary when welding thin pieces and delicate metals. Thin metals don't need too much heat; you instead need to control it.

Using smaller-diameter wire allows you to weld thin metals safely without burn-through or distortion. However, using too much heat with thin wires can cause them to evaporate and spit around the workplace. Therefore, you should always weld within the recommended limits.

MIG Welding Thin Metal Auto Body Panels
Source: https://www.youtube.com/watch?v=Ih9IXymXP48

MIG Wire Sizes And Deposition

The size of the MIG wire can affect the deposition rates. The deposition is the amount of filler metal transferred into the weld joint, and the properties of the MIG wire's filler metal dictate the depositions.

If you think logically, the larger the wire is, the more weld metal you get as it melts. The more molten metal you get for a specific time, the higher the deposition is. High deposition is particularly helpful when filling larger joints or thick sections of stock metal.

Filling Large Gaps with MIG Welding
Source: https://www.youtube.com/watch?v=xCZz1l0Ip1Y

However, that's not the only application. Some welders use larger MIG wire to finish the job on thinner metals quickly. As long as you control the heat, using the larger wire can help you fill the joint really fast. But keep in mind that you would sacrifice the precision that way and increase the risk of overwelding, slag inclusions, or burn-through.

Smaller diameter wires have lower deposition rates. They work great on smaller joints of thin metals, where precision and weld bead control are crucial. Limited heat reduces the risk of burn-through, and you correctly fill the tiny gap without the risk of excessive reinforcement or overwelding.

MIG Welding Thin Metal
Source: https://www.youtube.com/watch?v=X4WkDDnvS7g

MIG Wire Size and Welding Position

You can MIG weld in four primary welding positions, including flat, horizontal, vertical, and overhead. Here are some general rules that affect MIG wire sizes:

• Flat position: This is the most basic position. You weld on top of the welding joint, as the face is horizontal. Gravity works for you, and you can follow the wire size recommendations for the given metal thickness and amperage. In addition, you can even use a slightly larger wire to fill the joint quickly. Gravity will assist the deposition and provide the proper tie-in and fusion.

MIG Welding in Flat Position
Source: https://www.youtube.com/shorts/s_tvdlT0uK4

• Horizontal position: Welding in a horizontal position involves placing pieces horizontally and welding on the side. Gravity tends to pull the puddle to the lower edge of the joint. To deal with this, you should use a smaller-diameter wire to favor the upper side of the joint. That way, you prevent undercutting the upper edge or overlapping the lower edge.

MIG Welding in Horizontal Position
Source: https://www.youtube.com/watch?v=gPPvzKd3J5s

• Vertical position: Vertical MIG welding is a highly challenging task. As you weld up or down the joint, gravity pulls down the molten metal, so you have to adjust the parameters. To battle gravity, you should use a smaller diameter MIG wire, lower amps, and higher speed. The smaller wire will help you control the weld puddle, while lower amps and higher speed will help with solidification and weld cooling. The faster the puddle freezes, the lower the risk of defects.

Vertical MIG Welding Process
Photo by @premiumaccounts43 (TikTok)

• Overhead position: Overhead welding is the most challenging procedure in any welding method. A fluid weld puddle can drip on your welding helmet or escape the joint, so you should be very careful. To address these issues, you should use the smallest possible MIG wire size that still produces enough heat and penetration and a manageable weld pool size. 

Overhead MIG Welding Steel Components
Source: https://www.youtube.com/watch?v=elFdJTdgFbY

Joint Configuration And Wire Sizes

There are several types of weld joint configurations, with the most common being butt joints, lap joints, Tee joints, corner joints, and edge joints. The joint configuration with the thickness of the metal affects the gap between the two pieces. The bigger the gap is, the more weld metal you'll need; ergo, the larger the diameter of the wire.

For example, larger butt joints typically require more weld metal and, therefore, larger MIG wire to fill the gap evenly. Meanwhile, in the lap joint or edge joint, there is little to no gap. As a result, you can use the electrode recommended for the given metal thickness. Tee joints require a bit more weld material, but you can stick to the recommended wire sizes

MIG Welding on Four Essential Joints
Source: https://www.youtube.com/watch?v=cvME6dJIXN4&t

Wire Size And Weld Quality

Choosing the right MIG wire size for the given application can significantly affect the quality of the weld. The correct size will produce uniform and strong welds with no structural defects such as lack of penetration, fusion, or poor tie-in.

Additionally, there will be less excessive spatter, significantly reducing the time spent on post-weld cleaning. By reducing rework and post-weld cleaning, you will achieve higher efficiency, which is crucial in large-scale MIG welding applications such as industrial or automated MIG welding.

Automatic MIG Welding Process
Source: https://www.youtube.com/watch?v=ySUclPubh0Y&t

MIG Wire Size and Welder Limitations

When buying a MIG wire, make sure your welder and, more importantly, your welding gun and liner support the wire diameter. Most hobby and home welders, such as YesWelder MIG250 Pro, support MIG wires up to .035" and are rated up to 250 amps. If you use a larger diameter, you might run into several issues.

YesWelder MIG-250PRO-DG MIG Welder

Firstly, the torque of the wire feeding mechanism won't be strong enough to push the large-diameter wire. The wire would overflow the rolls, resulting in tangling, birdnesting, or a complete failure of the wire feeding mechanism.

Even if the high-quality mechanism pushes the wire, it next reaches the liner. If the liner is not large enough, the wire can tangle or clog it on its way. Finally, the MIG gun should be able to handle the wire diameter and, more importantly, the heat it produces.

Large-diameter wires over .040" require more than 300 amps. If your welder's power is insufficient to melt the wire, your MIG gun can overheat. Regular MIG guns are rated at 200- 250 amps. Therefore, using higher heat for a prolonged period can cause intense heat buildup, potentially permanently damaging your MIG gun.

Vertical MIG Welding with .045″ Flux-Cored Wire
Photo by @c_howwelds (TikTok)

What Happens When You Choose a MIG Wire That Is Too Large for Your Application?

You can sometimes use a larger diameter wire than recommended to achieve a higher deposition rate. However, several issues can emerge that you should be aware of, with the most important being:

Large weld bead that is harder to control: Larger wires produce a larger welding bead that can be harder to control, especially for beginners. Poor weld pool control can cause a lack of fusion and improper tie-in, even if you are transferring more weld metal into the weld joint. Also, a large puddle is unfavorable when MIG welding overhead or vertically.

Slag inclusions: Within a large weld puddle, slag can roll ahead and get trapped inside the weld. This issue is known as slag inclusion, in which the slag contaminates the weld’s composition. Non-metallic or other particles of slag can get trapped under the weld toe, and weld bead issues can result in a cold lap.

Slag Inclusions in Welding
Source: https://tft-pneumatic.com/blog/identify-welding-defects/

Increased shielding gas consumption: Larger wires have larger diameters and require higher shielding gas flow rates. More gas provides better shielding. Thus, when MIG welding with larger wires, ensure you have enough gas left in the tank to finish the job.

Overweld (Excessive reinforcement): Applying too much filler metal produced by a large-diameter electrode can create excessive reinforcement. This is a welding defect involving excessive weld metal, mostly on top of the joint. At its core, overwelding will significantly increase the costs, while it won't yield stronger welds.

Equipment limitations: You should never run a wire size that your MIG welder or accessories cannot handle. A wire that is too large can cause feeding issues, clogging, bird nesting, or even damage to the entire system. Additionally, large wires require high heat to run. Thus, they can cause overheating or damage to your MIG torch and welding machine.

Bird Nesting in MIG Welding
Source: https://www.youtube.com/watch?v=ySUclPubh0Y&t

What Happens If You Use a MIG Wire That Is Too Small for Your Applications?

Welders can use smaller wires when welding thicker pieces than recommended to increase precision. Smaller diameter MIG wires create a smaller weld puddle, which is easier to see and control. But keep in mind that the following issues can occur:

Lack of penetration: Smaller diameter wires transfer a limited amount of energy. As a result, if you try welding thicker pieces with thin wire, you can get a lack of penetration. A lack of penetration is a defect that occurs when the weld metal doesn't successfully penetrate the weld joint. The weld just sits on top of the joint, and weld failure is inevitable.

Lack of Penetration in Welding
Source: https://www.youtube.com/shorts/Z9p3yNMJ7uQ

Lack of fusion: Another defect caused by a lack of heat, caused by a too-small MIG wire, is a lack of fusion. It occurs when the wire's heat is not high enough to melt the base metal. A small void zone or gap appears between the weld metal and the sidewall, as well as a root opening or previous pass in multi-pass welding. This gap affects the structural integrity and creates a weak spot inside the weld.

Low efficiency: Filling larger joints with a smaller diameter wire can be time-consuming and inefficient. Even if you manage to get enough heat to penetrate the metal with a thin wire, it might take much more time and wire to fill the joint. This is particularly unfavorable in mass-production industrial applications.

Arc issues: Running too much heat through a small-diameter wire can cause arc formation issues. If you over-tune the machine while using a too-small wire, the wire will "evaporate," stick to the nozzle, or spit all around the workplace.

Excessive heat on small-diameter MIG wire causes burnback.
Source: https://blog.binzel-abicor.com/usa/solving-welding-burnbacks-in-robotic-applications

Quick Tips on How to Choose the Right MIG Wire Size

As a summary of everything we said in the article, we present you with some quick tips on how to choose the correct MIG wire diameter:

MIG Welding Process
Photo by @j_xanderrr (TikTok)

• Consider the metal thickness: Always select the MIG wire size based on the thickness of the parent metal. Use our wire size chart or the manufacturer's recommendations to make the right choice. Alternatively, use a smart function on a MIG welder.
• Ensure your welder can handle the wire: Always work within your welder's limitations to ensure proper wire feed and prevent damage to the parts.
• Consider the welding position and joint configuration: You can use one size larger wire in a flat position, and butt welds to finish the job faster. Welding overhead or in a vertical position requires a smaller diameter wire, less heat, and a faster speed.

Vertical MIG Welding in Action
Source: https://www.youtube.com/watch?v=CPvwecz1dAk

• Look for penetration and fusion. Proper penetration and fusion are signs that you have chosen the MIG wire size correctly. If you need deeper penetration, increase the size, and if you want more shallow penetration, decrease the size.
• Visually inspect welds: Strong welds are uniform and evenly distributed across the joint, and they have a flat profile. Bumps or small hills on your welds indicate you might be using too large wire and overwelding.
• Consider deposition: Larger wires transfer more weld metal into the joint, increasing the deposition. Use them when you need to finish the job quickly. Small wires promote precision.
• Consider the shielding gas: Larger wires produce a larger weld puddle. That means you'll need a higher shielding gas flow rate to protect the wire and puddle from contamination.

Recommended Shielding Gas Flow Rates Based on Nozzle and Wire Size

Bonus Tips When Choosing the MIG Wire

• Bonus tip 1: Match the composition to the base metal. Use mild steel wire when welding mild steel, aluminum wire for aluminum, and stainless steel wire for stainless steel.

• Bonus tip 2: Use the right shielding gas for your wire. Mild steel wires can run on Argon, Argon/CO2, or a pure CO2 mixture. When MIG welding aluminum, always use pure Argon, or add Helium for thicker aluminum pieces. Stainless steel wire requires a blend of Argon and O2 or a tri-gas mixture of Argon, Helium, and CO2.

• Bonus tip 3: Select the right-sized and grooved drive rolls. Adjusted tension and good drive rolls will provide proper wire feed. Good wire feed is as important as choosing the correct MIG wire.

MIG Welding Process
Photo by @kingstonwelding (TikTok)

 

 

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