Welding Wire Diameter: Your Key to Perfect Welds


Many people consider welding wire to be a relatively insignificant part of the welding process—something that you can just pick up and start using without much worry about quality or effect. But welding wire is actually pretty darn important; it has a profound effect on weld quality and weld strength. Welding wire is the filler metal that you use to bridge the gap between two base-metal pieces being joined together with heat. And because the wire is the material being added to the joint, and because it is also a part of what is going to hold the two base-metal pieces being joined together when it cools and solidifies, it is of the utmost importance to use the right kind of welding wire for the job and to use it in the right amount and in the right way.

Understanding Welding Wire Diameter

What is welding wire diameter? It is just the thickness of the wire. People typically use inches or millimeters to describe this thickness. What thickness should you choose? The welding position matters. The base material matters. The desired weld penetration matters. The type of welding process matters. All these factors impact the choice of wire thickness that should be used.

The importance of welding wire diameter

The thickness of the welding wire used affects several key factors in the welding process. For one, the heat input is greater when thicker wire is used. This obviously can affect the appearance of the weld, but there might not be a big difference if the amperage and arc time are the same. However, when it comes to penetration, thicker wire does a better job. Thicker wire can also be used to weld faster while still getting good penetration, but that’s a discussion for a different time.

Factors Influencing Welding Wire Diameter Choice

  1. Thickness of the base material is the most critical factor you will consider when selecting a wire size. When a weld is created, the joining of two pieces of material can occur at the faying surface, but it also has to occur deep in the joint. If the base material is thicker, the weld is going to need more filler metal to create a weld that has both adequate penetration and adequate strength.
  2. A weld being made using the TIG process, typically requires only a little bit of fill material, compared to  MIG. Even so, and with a little finesse, it is entirely possible to make TIG welds that possess a little more “meat” for the times when a little more strength is desired.
  3. When wire size is too small, insufficient penetration into the base material occurs. In some respects, it’s kind of like driving a 16-penny nail into a 2 x 4. Yes, it can be done, but it’s not always the best choice.

Choosing the Right Welding Wire Diameter

When it comes to the relationship between welding wire and welding material thickness, you can think of it in simple terms. If the material you’re welding is thin, use a thin wire. If it’s thick, go for a thick one. And if it’s in between, you guessed it; use a wire in between. Here are some more specific recommendations:

Welding wire comes in different thicknesses, and as you might expect, the thicker the wire, the more amperage it can handle. The amperage that appropriate arc welding requires varies depending on what you are doing and on the situation. But even if you try to keep everything constant, the heat developed and delivered to the work being welded can be a little different, particularly when you’re using different thicknesses of wire.

Helpful Suggestions for Choosing the Right Welding Wire

  • Please refer to the welding charts kindly provided by the wire manufacturers or welding equipment suppliers. Those charts are really nice because they give you recommendations of wire diameters based on the material thickness you’re welding and the kind of welding process that you’re using.
  • Ultimately, when it comes down to it, if you don’t feel like you’re getting the right amount of burn-in or if you don’t like the way it looks when it’s finished, go up or down by a tenth and see how that works. Because a lot of times, that might just be the little tiny adjustment that you need to make to get a good, positive feel of how the wire feeds, how it’s burning in, if it’s burning in the right amount, and if it’s finishing up clean.
  • Now, truth be told, if you really don’t have the time to do that, because sometimes those little adjustments can take a whole lot of time just to figure out.


The step toward selecting the right welding wire diameter can greatly affect the success of a weld. The decision requires an understanding of all the factors at play and the way they can or should influence the choice you make. You must follow the guidelines, too, if you’re to be confident about your wire-diameter choice. With all this in mind, you can be assured that you’re headed into territory where the wire you choose to weld with is of the right size, quality, and kind to make the weld pool do what you want it to do.

Find more information about welding wire and welding techniques at  UDO website –

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