Welding Amperage Calculator
Find a starting amperage for stick, MIG or TIG from the electrode or wire size and the material thickness, with wire feed speed and voltage.
How to use this calculator
- 1Enter the thickness of the thinner part. Setting for the heavier member is how the lighter one gets a hole in it.
- 2Take the range as a starting point and run two beads on scrap of the same thickness. That will tell you more than any chart.
- 3Listen to the arc. A steady crackle is right; popping and spitting is cold, and a digging, undercutting arc is hot.
- 4Read the packet. The manufacturer tested that consumable, and where the packet and this page disagree, the packet is right.
How the calculation works
Stick: about 1 amp per 0.001 in of core diameter, then adjusted by the coating
MIG: about 1 amp per 0.001 in of material, bounded by the wire size window
MIG wire feed = melting rate / wire weight per inch, melting rate about 0.0246 lb/hr per amp
TIG: 1 amp per 0.001 in in steel, about 1.4 in aluminium
Out of position: about 12 to 15% less- Core diameter
- The wire inside a stick electrode, not the coated outside diameter
- Melting rate
- How fast the arc consumes wire, roughly proportional to current for a given wire
- Position factor
- Out of position the puddle has to stay small enough to support itself, so the current comes down
The melting rate constant reproduces the published MIG settings charts: 0.035 in wire at 200 A comes out near 300 in/min, which is where the charts put it, and 0.045 at 300 in/min gives about 8 lb/hr, which is the trade figure.
Melting rate is not exactly proportional to current - resistive heating in the electrode stickout adds a term that grows with stickout length - so a long stickout melts wire faster at the same current.
A MIG machine has no amperage control. Current is an output, set by how fast wire is fed into a fixed-voltage arc, which is why the ammeter moves when only the wire speed knob is touched.
Worked example
1/8 in 7018 on quarter-inch plate
- 1.A 1/8 in rod is 125 thousandths, so the rule of thumb puts it near 125 A.
- 2.The published band for 1/8 in 7018 is 110 to 165 A - higher than the rule of thumb, because low-hydrogen coatings need a fluid puddle to float the slag out.
- 3.Flat position, so no reduction, and the midpoint is about 138 A.
- 4.Quarter-inch material at one amp per thousandth would suggest 250 A, which is far more than a 1/8 rod can carry - on plate this thick that means more passes, not more current.
Result: About 138 A, in a 110 to 165 band
The same rod overhead
- 1.Nothing changes about the electrode or the material.
- 2.But overhead the puddle has to be small enough that surface tension holds it against gravity.
- 3.Taking about 15% off gives roughly 94 to 140 A, with a midpoint near 117.
- 4.Run it hotter than that and the puddle grows past what surface tension will hold, and it comes down on the welder.
Result: About 117 A - 15% down from flat
MIG on 1/8 in sheet
- 1.An eighth of an inch is 125 thousandths, so about 125 A - comfortably inside what 0.035 wire carries.
- 2.At 125 A the wire burns off at roughly 0.0246 x 125 = 3.08 lb/hr.
- 3.A 0.035 wire weighs 0.000273 lb per inch, so that is 3.08 / (60 x 0.000273) = 188 in/min of wire feed.
- 4.Short circuit transfer, so 17 to 22 V - and the machine has no amperage knob, because the current is whatever the wire speed demands.
Result: About 125 A at 188 in/min, 17 to 22 V
What amperage actually controls
Current sets how much metal melts per second, and therefore how big the puddle is and how deep it penetrates. Everything else about the setting follows from managing that puddle: enough to fuse both members and carry the filler in, not so much that it falls through the joint or runs out of the groove.
That is why thickness is the primary input. A thick section conducts heat away fast and needs a lot of energy to reach fusion at all; a thin one has nowhere to put the heat and reaches melting almost immediately. The rough equivalence of one amp per thousandth of thickness works across a surprisingly wide range for exactly that reason.
It is also why position matters. A puddle is liquid metal held in place by surface tension, and out of position surface tension is all there is. The puddle has to stay small enough to hold itself up, which means less current and a faster, tighter technique.
Why MIG has no amperage knob
A stick or TIG machine is constant current: it holds the amperage where the dial is set and lets the voltage float as the arc length changes. A MIG machine is the opposite - constant voltage. It holds the voltage and lets the current do whatever it must.
What that means in practice is that the current is set by the wire feed speed. Feed wire faster into a fixed-voltage arc and the arc has to melt it faster, which it does by drawing more current. The ammeter on the front of a MIG machine is reporting an outcome, not a setting.
This is genuinely useful once it clicks, because it makes the arc self-correcting. If the torch drifts closer to the work the arc shortens, the voltage across it falls, the current spikes, and the wire burns back to restore the length - all within milliseconds and without the welder doing anything. It is why MIG is so much easier to learn than TIG, and why the two knobs on the front interact in ways that confuse everyone at first.
- Wire speed — Sets the current. More wire needs more amps to melt it.
- Voltage — Sets the arc length and the bead shape. Higher is flatter and wider.
- Too cold — Stubbing - the wire pushes into the plate before it melts. Raise voltage or lower wire speed.
- Too hot — A long, wandering arc and a lot of spatter. Lower voltage or raise wire speed.
Listening to the arc
Every experienced welder sets by sound before they set by numbers, and the reason is that the sound reports on what is actually happening at the arc rather than on what the machine was asked for.
Short-circuit MIG at the right settings sounds like frying bacon - a fast, even crackle at a hundred-odd shorts a second. Slow it down and the crackle becomes a series of pops as each short takes longer to clear. Speed it up too far and it becomes a hiss with a lot of spatter, because the wire is burning back rather than shorting.
Stick at the right current has a steady, even crackle and the rod feeds smoothly. Too cold and the rod sticks, the arc pops and goes out, the slag will not release. Too hot and the arc gets loud and wide, undercut appears along the toes, and the rod turns red and starts throwing its coating off before it is half consumed. That last symptom is the most reliable single indicator that a stick machine is set too high.
What this assumes, and where it stops
Assumptions
- Amperage bands are typical published ranges for common consumables. Specific brands vary and the packet is authoritative.
- The MIG melting rate constant is a first-order fit that reproduces published settings charts; real melting rate also rises with electrode stickout.
- Position adjustments are typical practice rather than a code requirement.
- The one-amp-per-thousandth rules are starting points for common carbon steel work, not universal constants.
Limitations
- It does not choose the process or the joint preparation, both of which matter more than the amperage setting.
- Multi-pass welding on thick sections is governed by the procedure and by interpass temperature, not by a single current figure.
- Aluminium, stainless, cast iron and coated steels all behave differently from carbon steel, and coated steels release fume that changes the safety picture entirely.
- Pulsed and waveform-controlled machines set their parameters as a package, and a plain amperage figure does not describe them.
- Any welding to a code needs a qualified procedure, and the procedure specifies the ranges - not a chart.
Common questions
What amperage for a 1/8 inch 7018 rod?
Between about 110 and 165 amps, starting near 130 to 140 flat. The rule of thumb of one amp per thousandth of core diameter would say 125, and low-hydrogen coatings run a little above that because the puddle has to stay fluid enough to float the slag out ahead of it. Overhead, take about 15% off.
How many amps per inch of thickness?
About one amp per thousandth of an inch, which is a thousand amps per inch - so an eighth of an inch is around 125 amps and a quarter is around 250. It holds up well to about a quarter inch. Beyond that, thick sections are welded in multiple passes rather than at ever-higher current, because a single enormous pass would put in far too much heat.
Why does my MIG machine not have an amperage setting?
Because it is a constant-voltage machine, and the current is an output rather than an input. You set the wire feed speed, and the arc draws whatever current it needs to melt that much wire. The ammeter is reporting the result. It also makes the arc self-correcting, which is a large part of why MIG is easier to learn than TIG.
How do I stop burning through thin sheet?
Less current, smaller wire or rod, and less continuous heat. Stitch the weld rather than running a continuous bead, let it cool between stitches, and back the joint with copper or aluminium where you can - a backing bar draws heat out of the puddle and will hold one that would otherwise fall through. On anything under about a sixteenth of an inch, stick is usually the wrong process.
Should I trust the chart on the machine door?
As a starting point, yes - it is usually reasonable. Trust the packet on the consumable over it, and trust two test beads on scrap of the same thickness over both. Charts cannot see your fit-up, your joint design, your gas, your stickout or your travel speed, all of which move the right answer.
Sources
- Filler metal selection and welding parameter guidance — Lincoln Electric
Formula and content last reviewed on .
Results are estimates for information only, not professional advice.
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