Most MIG problems aren't bad welders — they're bad starting numbers. Get amperage and wire feed close on the first arc and you spend the rest of the day adjusting fine instead of chasing your tail. This guide gives you starting points that actually land in the puddle on carbon steel, plus the math for when you're outside the chart.

The four numbers you actually set

• Voltage — sets arc length and shape
• Wire feed speed (WFS) — sets amperage on a CV (constant-voltage) MIG machine
• Gas flow — sets shielding (15–25 CFH typical)
• Travel speed — sets bead width and heat input

On a CV machine, the welder regulates voltage and you regulate WFS. Amperage isn't a knob — it's an outcome of WFS, wire diameter, and contact-tip-to-work distance. Push the wire faster, the machine delivers more current.

Carbon steel starting numbers (short-circuit, 0.035" wire, 75/25 gas)

• 22 ga (0.030") — 17–18 V · 90–110 IPM WFS · 35–55 A
• 18 ga (0.048") — 17–18 V · 130–160 IPM · 50–80 A
• 16 ga (0.060") — 18–19 V · 160–200 IPM · 80–110 A
• 14 ga (0.075") — 18–19 V · 200–250 IPM · 110–135 A
• 1/8" (0.125") — 19–21 V · 240–300 IPM · 130–165 A
• 3/16" (0.188") — 21–22 V · 290–340 IPM · 170–200 A
• 1/4" (0.250") — 22–24 V · 320–380 IPM · 200–230 A

Above 1/4" plate switch to spray transfer (24–28 V, argon-rich gas like 90/10 Ar/CO₂ or 98/2 Ar/O₂) for hot, fast deposit rates. Short-circuit can be done above 1/4" but you need multiple passes and you're fighting cold lap.

Wire size by thickness

• 0.024" — sheet, 22–18 ga, light fab
• 0.030" — body and frame, 18–14 ga
• 0.035" — the workhorse: 14 ga to 1/4"
• 0.045" — heavy plate, structural, 1/4" and up

The amperage-from-WFS math (carbon steel)

Cheat-sheet conversion if your machine only shows wire feed speed:

Approximate amps for ER70S-6 on carbon steel:

  0.030" wire:   amps ≈ WFS (IPM) × 0.41
  0.035" wire:   amps ≈ WFS (IPM) × 0.55
  0.045" wire:   amps ≈ WFS (IPM) × 0.85

Example: 0.035" wire at 250 IPM
  amps ≈ 250 × 0.55 ≈ 138 A

These are for short-circuit on carbon steel with a 3/8" stickout. Spray transfer numbers run higher because the arc is longer and the droplets cross faster.

Gas selection cheat sheet

• 75/25 Ar/CO₂ — default for steel short-circuit. Good wetting, mild spatter.
• 90/10 Ar/CO₂ — spray-transfer carbon steel above 1/4". Hotter, smoother arc.
• 100% CO₂ — cheap, deep penetration, more spatter. Repair work, dirty material.
• 98/2 Ar/O₂ — spray transfer on stainless / harder steels. Stable arc, low spatter.
• Tri-mix (He/Ar/CO₂) — stainless: better wetting + lower distortion than 98/2.

Heat input — the number that matters for code work

Heat input controls HAZ properties. Structural codes (AWS D1.1, ASME) cap it for procedure qualification. The formula:

HI (kJ/in) = (V × A × 60) / (TS × 1000)

V  = volts
A  = amps
TS = travel speed (in/min)

Example: 200 A · 22 V · 12 IPM travel
HI = (22 × 200 × 60) / (12 × 1000)
   = 264,000 / 12,000
   = 22.0 kJ/in

Most carbon-steel structural welds want 15–55 kJ/in of heat input. Below that you risk under-bead cracking on hardenable steels. Above that you grow grain and lose toughness.

Reading the puddle

• Buzzy, popping arc — voltage too low for the WFS. Bump volts up 1–2.
• Long, soft arc with no fusion at toes — voltage too high. Drop volts.
• Tall, ropy bead — travel too slow OR amps too low. Speed up first.
• Burn-through on sheet — too hot OR too slow. Drop WFS, speed up, or both.
• Wire stubbing into work — WFS way too low for the volts.
• Wire burning back to tip — WFS too low or stickout too short.

Common mistakes

• Welding with too short a stickout (< 1/4"). Splatter eats the nozzle in minutes.
• Welding with too long a stickout (> 3/4"). Lose shielding, get porosity.
• Setting WFS without checking volts. Voltage and WFS are a couple — they move together on a sync chart.
• Running 75/25 gas above 1/4" plate. Switch to 90/10 and go to spray.
• Ignoring the contact tip. A worn or wrong-size tip ruins everything else you set.

Run it on your phone

The WelderCalc app does all of this — amperage starting points by wire/material/thickness, heat input calculator, multi-pass planner, fillet weld strength, gas flow, carbon equivalent and preheat for hardenable steels. 100% offline, free on the App Store and Google Play.

Related

• WelderCalc — welding calculator on iOS + Android
• Speeds and feeds for CNC machining

Note: Starting points only. Always run a coupon test before production work, follow your WPS for code welds, and trust your eyes and ears over any chart.