Plasma Cutter Buying Guide: Size Amps, Air, and Duty Cycle
By MIG/TIG/Stick Welders & Plasma Cutters | USA Weld – HTP ... | Published: 2026-10-16
Category: Buying Guides
Size a plasma cutter by clean-cut thickness, not marketing amps. Learn how amperage, air requirements, and duty cycle work together before you buy.
Quick answer
Size the machine to the thickest metal you will cut regularly, not the thickest you might cut once. As a working rule, a 30-40A plasma cutter handles 1/4 in. steel, 40-50A covers 3/8 in., and 50-60A covers 1/2 in. on a clean cut. Then confirm your compressor can deliver the required CFM at the rated pressure, because an undersized air supply is the most common reason a new plasma cutter underperforms.
Start with clean-cut thickness, not severance
Severance thickness is the absolute maximum the torch can push through, and the cut quality at that limit is rough. Clean-cut thickness is what you can actually use for fabrication, brackets, and trailer repairs. A 40A machine that cleanly cuts 3/8 in. will serve a home shop better than a 50A unit that only severs 1/2 in. and leaves dross on every pass. If most of your work is 1/8 in. to 1/4 in. sheet and plate, a 30-40A machine is usually the right size, and it will run on a 240V circuit without tripping a 50A breaker.
Match air pressure and CFM to the cut chart
Every plasma cutter has a required air pressure range and a minimum CFM at that pressure. A 40A machine typically needs about 4-6 CFM at 60-80 PSI, while a 60A machine can demand 6-9 CFM at the same pressure. Check the compressor's CFM rating at 90 PSI, not the tank size. A 20-gallon compressor with a high CFM pump can outperform a 60-gallon unit with a low CFM rating. Moisture is the other half of the air requirement: plasma cutting needs dry, clean air, so a refrigerated dryer or a desiccant filter is not optional in humid climates.
Read the duty cycle before you buy
Duty cycle is the percentage of a 10-minute period the machine can run at a given amperage before it needs to cool. A 60% duty cycle at 40A means six minutes of cutting, then four minutes of rest. If you cut long seams or run a CNC table, a 60% duty cycle will stop you repeatedly; a 100% duty cycle at your working amperage is worth the extra cost. For occasional home shop work, 40-60% is usually fine. The duty cycle drops as amperage rises, so compare machines at the amperage you will actually use, not the peak rating.
Budget for consumables and torch support
Electrodes, nozzles, and shields wear out, and the cost per cut depends on how well you manage air quality and pierce height. Cheap consumables often fail early and can damage the torch. Before buying, confirm that consumables and replacement torches are stocked in the sizes you need, and that the torch uses a standard connection rather than a proprietary one. A machine with widely available consumables will cost less to own over five years than a cheaper machine with hard-to-find parts.
Check the power supply and portability
Most 30-50A plasma cutters run on 240V single-phase and draw 20-30A, so a 50A circuit is usually sufficient. Some dual-voltage machines can run on 120V at reduced output, which is useful for thin sheet but not for 3/8 in. plate. If you need to move the machine around a shop or load it into a truck, weight and a shoulder strap matter more than a digital display. A 40A unit that weighs 25 lb. will get used more than a 60A unit that stays in the corner.
Decision rules for sizing your plasma cutter
- Rule 1: Match amps to your daily thickness: If 90% of your cuts are 1/4 in. or thinner, buy a 30-40A machine. If you regularly cut 3/8 in., step up to 40-50A. For 1/2 in. production work, choose 50-60A and confirm the duty cycle at that amperage. Write down your three most common thicknesses before comparing models.
- Rule 2: Size the compressor to the cutter's CFM: Find the cutter's required CFM at its rated pressure, then add 20% headroom. A compressor that barely meets the minimum will run continuously and send hot, wet air to the torch. Check the compressor's CFM at 90 PSI, not tank gallons.
- Rule 3: Duty cycle decides long cuts: For cuts longer than 4-5 minutes at full amperage, choose a machine with at least 60% duty cycle at that amperage. For occasional short cuts, 40% is acceptable. If you plan to add a CNC table later, buy 100% duty cycle now.
- Rule 4: Verify consumable availability: Before buying, confirm that electrodes, nozzles, and shields for that torch are in stock in the sizes you need. A machine with a proprietary torch can become unusable if consumables dry up. Buy a spare set of consumables with the machine.
Product facts that affect the cut
- 26 Series (200A) Air-Cooled Torch w/35 Dinse & Flow Thru Gas: 26 Series (200A) air-cooled TIG torch with a 35 Dinse (1/2 in. OD) power connection and flow-through gas. If you also TIG weld, a torch with a standard Dinse connection and flexible cable reduces wrist strain and lets you switch between processes without adapter hunting.
- Super-Flex Power Cable for 9 & 17 Series Air-Cooled TIG Torches: Super-Flex power cable for 9 and 17 Series air-cooled TIG torches, available in 12.5 ft. and 25 ft. lengths with 3/8-24 RH male connections. A silicone rubber cable with a nylon braided overlay stays flexible in cold weather, which matters if your plasma table or welding bench sits in an unheated garage.
- Steel Liner, 15': 15 ft. steel liner with a 3/8 in. large diameter and 9/32 in. small diameter, brass alloy stop, and zinc-plated spring wire. If you also run MIG, a liner sized to your wire diameter prevents feeding problems; the zinc plating resists corrosion in humid shops.
Who should buy which size
Best for
- Home shop and garage fabricators cutting 1/8 in. to 1/4 in. steel, who want a 30-40A machine on a 240V 50A circuit
- Farm and trailer repair work with occasional 3/8 in. plate, where a 40-50A machine with a 60% duty cycle covers most jobs
- Small production or CNC table users cutting 1/2 in. regularly, who need 50-60A and 100% duty cycle at working amperage
Not for
- Cutting 1 in. or thicker steel daily, which requires a larger industrial machine and a much larger compressor
- Shops with only a 120V circuit and no plans to add 240V, unless a dual-voltage machine's reduced output is acceptable
- Buyers who will not maintain an air dryer or filter, since moisture will shorten consumable life on any plasma cutter
