Minimum Amps for Steel Thickness: A Simple Chart

What minimum amps means on a welder listing

Amperage on a welder title is the output the machine can deliver, usually shown as a top figure such as 85 amps or 160 amps. Buyers often ask what the minimum amps are for a piece of steel, whether it is plate or tube, expecting a single rule that maps thickness to amperage.

The honest answer is that there is no universal rule. The same joint can be welded with a modest machine in some setups and by a higher-amp machine in others, because the process, the electrode or wire size, the shape of the joint and the number of passes all matter.

That is why this site compares listings on stated details instead of publishing an amp-to-thickness table; the best-welder guide is where that comparison lives. For more on reading output, see amp output ranges and which process for thick steel.

Maker-stated thickness capabilities for common steel

Notice that the listed amps and thicknesses come from the same maker pages, but they are not a formula. A 160-amp machine is stated for twice the thickness of an 85-amp machine, yet Miller states 1/2 in. capability on a multiprocess without giving a top amp figure on its home page. Read each maker's claim separately.

Why there is no simple amp-to-thickness chart

Welding a given thickness is not a single fixed amperage. MIG, stick and TIG each use the current differently: stick uses the electrode as the filler, MIG adds wire through the gun, and TIG uses a tungsten electrode with a separate filler rod. The maker pages describe these differences in general terms.

A thicker plate can often be welded in a single pass with more current, or in several passes with a smaller machine, depending on the joint and the setup. Choosing between those paths is a matter of technique and is outside what this site compares on listings.

The useful chart for a buyer is the one above, read as a starting point: find the thickness you plan to weld most, then compare machines whose maker pages claim at least that thickness. See multi-process welders for how one machine covers several processes, and the multi-process guide for a shortlist.

MIG and flux core: what the maker pages state

MIG welding uses a continuously fed wire as filler, with shielding gas around the arc. Flux core, sometimes called gasless, is the MIG-family process that uses a tubular wire with its own shielding, which is why it shows up on titles for outdoor repair work. The Weldpro page describes MIG as an arc welding process in which welding wire is applied as an electrode.

On the Forney page, a 120V flux core welder is stated for up to 3/16 in. steel, a class of machine that buyers pair with home garage and farm repairs. A 208-575V MIG and pulsed MIG machine from Miller is stated for up to 1/2 in. mild steel and aluminum.

For a first MIG machine, compare the stated thickness and the input voltage, and read the maker's manual for the wire sizes the machine accepts. The MIG guide and the 120V guide list machines by stated details.

Stick: what the maker pages state

Stick welding, also called arc welding or SMAW, uses a coated electrode as both the filler and the current carrier and needs no shielding gas, as the Everlast page explains.

The Forney pages give two stated claims to compare: a 120V stick and DC TIG welder that delivers up to 85 amps and is stated for 1/4 in. mild steel, and a dual-voltage stick and DC TIG welder that delivers up to 160 amps and is stated for portable 3/8 in. welding, with 6010 capability.

Stick machines in this class also list DC TIG in the title, so you can compare both processes on the same stated details. The stick guide covers this class of machine.

TIG: what the maker pages state

TIG welding uses a tungsten electrode to carry the arc and a separate filler rod when filler is added. The Weldpro page describes TIG as a high-quality, high-precision method used for stainless steel, aluminum and copper.

On the pages cited here, DC TIG appears on the same machines as stick: the 120V unit rated up to 85 amps for 1/4 in. mild steel and the dual-voltage unit rated up to 160 amps for 3/8 in. welding. A 208-575V multiprocess machine is also stated for DC TIG up to 1/2 in. mild steel.

For thin steel and stainless work, a TIG listing with a lower amp rating is often what buyers compare, but the stated thickness claim is the figure to read. The TIG guide and the 200-amp guide compare machines on stated details.

Questions to ask the maker before you pick

These questions are about reading a listing, not about welding technique. The answers come from the maker's official page and manual, which this site points to instead of publishing its own settings or rules.

See amp output versus input power for the two other numbers a listing shows.

• For the thickness you plan to weld, what is the stated capability with the supplied consumables, and what changes if you use a different wire or electrode size?
• Is the stated thickness claim for a single pass or for multiple passes?
• What input voltage does the maker's manual name for the thickness claim?
• Does the title list DC TIG, AC/DC TIG, or no TIG, and how does the listing describe it?
• What does the warranty cover, and where is the manual and service contact?
• Does the listing include a spool gun, foot pedal or other parts that change the stated capability?

What to read on a listing before you buy

Start with the process words on the title: MIG, flux core, TIG, stick, or multi-process. Then read the amp figure and the input voltage: 120V, 240V, dual voltage, or an industrial 208-575V range.

The thickness a maker claims is not usually on the title, so open the maker's official page and read the stated 'up to' figure. Compare only machines whose maker pages state at least the thickness you plan to weld.

For the exact minimum amps for your joint, the maker's manual is the authority. If you are taking a class, ask the instructor; the American Welding Society describes certification and education programs on its site.

This site leaves the amp-to-thickness decision to the manual because the same plate can be handled by different machines in different setups. The guides below list machines by stated details so you can build a shortlist.

What to pick for your situation

Questions

What thickness can a 120V welder handle?

The maker pages cited here state a 120V flux core welder for up to 3/16 in. steel and a 120V stick and DC TIG welder for up to 1/4 in. mild steel at up to 85 amps. Check the listing and the maker's manual for your exact machine.

Is there a chart of minimum amps per steel thickness?

No single chart works for every setup. Process, wire or electrode size, joint shape and pass count all change the requirement, so this site does not map amps to thickness. The maker-stated 'up to' thickness is what a listing can tell you.

Do I need a 200-amp machine for 1/2 in. steel?

Not necessarily. Miller states a 208-575V multiprocess for up to 1/2 in. mild steel and a 208-575V MIG and pulsed MIG for the same thickness, without stating a top amp figure on its home page. Compare the maker's stated claim and read the manual.

Which process uses more amps for the same steel?

MIG and stick can carry more current for thicker steel, while TIG is often used for thinner work, but the figures depend on the machine and consumables. The maker's manual is the place to read the actual range.

What does 'up to 1/2 in.' on a maker page mean?

It is the thickness the maker claims the machine can weld with its supplied consumables and settings. It is a stated capability, not a minimum amp figure, and the manual explains the conditions.