Spool Length and Arc Time
Wire Diameter by Amperage and Thickness
| Wire | Amp Range (short circuit) | Steel Thickness | Ft per lb (steel) | Typical Use |
|---|---|---|---|---|
| .023" | 30–130A | 24 ga – 1/8" | 706 | Auto body, sheet metal, small 120V welders |
| .030" | 40–145A | 22 ga – 3/16" | 415 | All-round 120V wire, light fab |
| .035" | 50–180A (to ~250A spray) | 18 ga – 1/4"+ | 305 | General 240V shop work |
| .045" | 75–250A (to ~350A spray) | 1/8" and up | 184 | Heavy plate, spray transfer, production |
MIG Wire Types
| Classification | Type | Gas | Use It For |
|---|---|---|---|
| ER70S-6 | Solid mild steel | 75/25 or CO2 | The default wire. Extra deoxidizers handle light mill scale and rust. |
| ER70S-3 | Solid mild steel | 75/25 or CO2 | Clean steel; slightly cleaner-looking welds, less tolerant of dirt. |
| E71T-11 / E71T-GS | Self-shielded flux core | None | Outdoor and windy jobs, rusty steel, small machines. Limited to thinner multi-pass work by spec. |
| E71T-1 / E71T-1C | Dual-shield flux core | CO2 or 75/25 | Heavy structural work, high deposition, all positions. |
| ER308L / ER316L | Solid stainless | Tri-mix or 98/2 | 304 and 316 stainless. |
| ER309L | Solid stainless | Tri-mix or 98/2 | Stainless to mild steel joints. |
| ER4043 | Aluminum (silicon) | 100% Argon | General aluminum, smoother flow, less crack-sensitive. Not for anodizing color match. |
| ER5356 | Aluminum (magnesium) | 100% Argon | Higher strength, marine, stiffer wire that feeds better. |
How to Choose MIG Wire Size
Wire diameter sets how much current the wire can carry and how much metal goes into the joint. Too thin a wire on thick plate means you hit the top of its range before you get penetration. Too thick a wire on sheet metal needs more current to melt than the sheet can take without blowing through. Pick the wire that puts your working amperage in the middle of its range.
.023" and .024"
For auto body panels, exhaust tubing and anything 18 gauge and thinner. The small wire melts at low current, so you can keep heat down and avoid warping. It is a poor choice past 1/8"; it simply can't carry enough current.
.030"
The best single wire for a 120V machine. It handles sheet metal and still welds 3/16" in a pass at the top of a small welder's output. If you only keep one spool on the shelf for a home shop welder, it should be .030".
.035"
The standard for 240V shop welders. It runs well from about 16 gauge up to 1/4" in short-circuit transfer and reaches into spray transfer on bigger machines. Most fabrication shops keep .035" ER70S-6 loaded.
.045"
For heavy plate and production welding on 250-amp-plus machines, usually in spray or pulsed-spray transfer with 90/10 argon/CO2. It puts down a lot of metal fast but is not practical on thin material.
Match the Consumables
The contact tip, drive rolls and liner all have to match the wire. A .035" tip on .030" wire gives an erratic arc; a .030" tip on .035" wire jams. Solid wire uses V-groove rolls, flux core uses knurled rolls so the soft tubular wire isn't crushed, and aluminum uses U-groove rolls with a Teflon or nylon liner.
How Long a Spool Lasts
A pound of .035" steel wire is about 300 feet. At 250 inches per minute that is roughly 14–15 minutes of arc-on time per pound, so an 11-pound spool gives around two and a half hours of actual welding. Real-world spool life is longer in calendar time because most of a welding day is fit-up, grinding and repositioning. Use the calculator above to plan wire for a job or compare the cost per foot of different spool sizes.
Frequently Asked Questions
.030" is better on 120V welders and thinner metal. .035" is better on 240V machines for 1/8" to 1/4" steel. If your welder tops out near 140 amps, use .030".
About 3,300 feet. Steel .035" wire runs roughly 300 feet per pound, so an 11 lb spool holds around 3,300 feet and a 2 lb spool about 600 feet.
ER70S-6 solid wire has the most deoxidizers for light rust and mill scale. For heavily rusted steel or outdoor work, self-shielded E71T-11 flux core handles contamination and wind better.
No. The contact tip must match the wire diameter. Oversized wire will jam in an undersized tip, and an oversized tip gives poor current transfer and an unstable arc.
ER70S-6 has more manganese and silicon deoxidizers, so it handles mill scale and light rust better and wets in more easily. ER70S-3 is best on clean steel.
