Plasma Cutter Amperage Calculator
Calculate plasma cutter amperage and travel speed for mild steel, stainless, and aluminum from material thickness.
Helps select machine and consumables.
Plasma cutting basics:
Plasma cutting uses an electrically conductive gas (compressed air, nitrogen, or argon/hydrogen mix) ionized into a plasma arc at 20,000–40,000°F to melt and blow through metal. The key parameter is amperage — higher amps cut thicker material.
Rule of thumb for mild steel:
Maximum cut thickness (inches) = Amperage ÷ 20
So a 60-amp plasma cutter can sever up to 3/4" mild steel (though clean cut capacity is lower — about 60% of sever capacity).
Amperage requirements by material and thickness:
| Material | Thickness | Recommended Amps | Cut Speed (IPM) |
|---|---|---|---|
| Mild steel | 1/8" (3 mm) | 25–30 | 80–120 |
| Mild steel | 1/4" (6 mm) | 40–45 | 40–60 |
| Mild steel | 3/8" (10 mm) | 55–60 | 25–40 |
| Mild steel | 1/2" (12 mm) | 65–80 | 15–25 |
| Mild steel | 3/4" (19 mm) | 80–100 | 8–15 |
| Mild steel | 1" (25 mm) | 100–125 | 5–10 |
| Stainless steel | Same thickness | +10–15% amps | 15–20% slower |
| Aluminum | Same thickness | −10% amps | 10–15% faster |
Material correction factors (vs. mild steel):
- Mild steel: 1.0 (baseline)
- Stainless steel: 1.15 (higher melting point, more heat resistant)
- Aluminum: 0.90 (lower melting point, but highly reflective)
- Copper/Brass: 1.30 (extremely high thermal conductivity draws heat away)
Cut quality factors:
- Clean cut capacity is typically 60–65% of maximum sever thickness
- Sever capacity means it will get through but with heavy dross and rough edges
- Faster speed = narrower kerf but potential for dross on bottom
- Slower speed = wider kerf, more heat input, potential warping
Worked example:
Cutting 3/8" mild steel with a 60-amp machine:
- Required amps: 55–60A (within machine capability)
- Recommended speed: 25–40 IPM
- Kerf width: approximately 0.06" (1.5 mm)
- Air pressure: 65–75 PSI at the torch
- Standoff distance: 1/16" to 1/8" (1.5–3 mm)
Consumable life:
At rated capacity, electrode and nozzle life is typically:
- Electrode: 1–2 hours of cutting
- Nozzle: 1–2 hours of cutting
- Shield cup: 4–8 hours
- Replace when cut quality degrades (wider kerf, excessive dross, arc wandering)
Air supply requirements:
Most plasma cutters need 4–6 CFM at 65–90 PSI. A small shop compressor (20+ gallon, 5+ CFM at 90 PSI) is the minimum. Moisture in the air line destroys consumables quickly — always use a moisture separator/dryer.