MIG welders run wire feed speed and amperage as effectively one control: the faster the wire feeds, the more current the arc draws to melt it. This calculator converts a target amperage into the wire feed speed your machine needs, and reports how fast you will deposit weld metal.
How it works
Each wire diameter has a published burn-off constant k in inches per minute
per amp. Wire feed speed and deposition rate are then:
WFS (in/min) = k(diameter) × amps
deposition (lb/hr) = WFS × 60 × wire_area × 0.2836 lb/in³ × efficiencyThe burn-off constant is larger for thinner wire because a smaller cross-section melts faster at a given current. Flux-core wire gets a small efficiency factor because it deposits slightly more metal per amp than solid wire.
Example and tips
Running 180 amps on .035 solid wire gives about 254 in/min of feed and roughly
6 lb/hr of deposition. If you switch to .045 wire at the same amperage the
feed speed drops to about 153 in/min because the heavier wire carries more metal
per inch. Always confirm settings on a scrap coupon: shielding gas mix, stickout,
and joint geometry all shift the ideal voltage and travel speed that pair with
these feed numbers.
Understanding the wire diameter trade-off
Choosing a wire diameter is a balance between deposition rate, penetration, and position:
| Wire size | Best for | Notes |
|---|---|---|
| .023 in | Sheet metal, thin gauge | Low heat input, tight control; low deposition rate |
| .030 in | Light structural, general fabrication | Good all-around; lower amperage range |
| .035 in | Most common structural size | Wide operating range, easy burn-through avoidance |
| .045 in | Heavy plate, high deposition | Needs higher amperage; not suited to thin material |
| .052 in | Very heavy plate, horizontal or flat only | High deposition rate; difficult out-of-position |
For out-of-position welding (vertical, overhead), choose a smaller wire diameter: the lower deposition rate gives better puddle control. For flat or horizontal welds on thick plate where throughput matters, step up to .045 or .052 to maximize deposition rate.
Feed speed and amperage: which drives which
On a constant-voltage (CV) MIG machine, you set wire feed speed and the machine self-adjusts voltage to maintain a stable arc. Faster feed pulls more current; the relationship is nearly linear for a given wire diameter and stickout. This is why feed speed is the primary amperage control on most MIG welders — the amperage dial on a CV machine is actually adjusting feed speed.
On a constant-current (CC) machine (more common with TIG), amperage is set directly and feed speed must match the melt rate. The two parameters are coupled differently, which is why the feed speed calculator is primarily a MIG tool.
Shielding gas effects
The burn-off constant also shifts slightly with shielding gas composition. A higher CO₂ content (e.g. C25 or C100) runs hotter and tends to require slightly lower feed speed at the same amperage to avoid a harsh arc. Pure argon (for aluminium or stainless) is cooler and the burn-off constant is somewhat lower. The figures this calculator uses are calibrated for carbon steel with C25 (75% argon / 25% CO₂) — the most common gas mix for solid ER70S wire. Expect small adjustments if you run a different gas.