MIG wire size by material thickness
Thinner wire gives finer control and less heat, which is what thin sheet needs. Thicker wire deposits faster on heavy plate but will blow straight through bodywork.
If you only buy one size for general work, 0.030 inch is the compromise. It handles most of what a workshop sees and still behaves on 18 gauge.
| Wire dia | Metric | Material range | Best at |
|---|---|---|---|
| 0.023 in | 0.6 mm | 24 ga to 1/8 in | Bodywork and thin sheet |
| 0.030 in | 0.8 mm | 22 ga to 1/4 in | General workshop |
| 0.035 in | 0.9 mm | 20 ga to 3/8 in | Fabrication and trailer work |
| 0.045 in | 1.2 mm | 1/8 in and up | Heavy plate, spray transfer |
MIG settings starting points
Every machine reads slightly differently, so treat these as a place to start and then tune by sound. A correctly set short-circuit arc makes a steady crackle like frying bacon. A hiss or a popping means the voltage or wire speed is out.
Adjust voltage first to set the arc length, then wire speed to set the burn-off rate. Too much wire speed pushes the wire into the puddle and stubs; too little burns back to the tip.
| Thickness | Wire | Voltage | Wire speed | Approx amps |
|---|---|---|---|---|
| 24 ga (0.6 mm) | 0.023 | 14 to 15 | 90 to 130 | 30 to 40 |
| 20 ga (0.9 mm) | 0.023 | 15 to 16 | 130 to 180 | 40 to 55 |
| 18 ga (1.2 mm) | 0.030 | 16 to 17 | 150 to 200 | 55 to 75 |
| 16 ga (1.5 mm) | 0.030 | 17 to 18 | 200 to 250 | 75 to 95 |
| 1/8 in (3.2 mm) | 0.030 | 18 to 19 | 250 to 300 | 110 to 130 |
| 3/16 in (4.8 mm) | 0.035 | 20 to 21 | 270 to 330 | 140 to 170 |
| 1/4 in (6.4 mm) | 0.035 | 21 to 23 | 300 to 380 | 170 to 200 |
Shielding gas
C25, which is 75 percent argon and 25 percent CO2, is the default for short-circuit welding on steel. It gives a soft arc, little spatter and a tidy bead.
Straight CO2 is cheaper and penetrates deeper but the arc is harsh and it spatters noticeably more. It suits heavy plate where appearance does not matter.
Higher argon mixes, around 90/10 or 98/2, are for spray transfer on thicker material at higher current. They will not run short-circuit well.
Flux-cored wire runs without gas at all, which is why it is the choice outdoors where any breeze strips the shield off a solid-wire weld. It leaves slag to chip.
