Technical reference

Fiber Laser Cutting Thickness and Speed Chart

Updated 2026-10-12 · 5 min read

Cutting speed and maximum thickness are the two numbers buyers ask about first, and the two that suppliers quote most loosely. Both depend on the material, the assist gas and how good the edge needs to be. This page gives indicative figures you can plan around, and explains why the same machine produces very different numbers in different shops.

Quick answer: For carbon steel in production, a 3 kW fiber laser cuts up to about 16–20 mm and a 6 kW machine up to about 25 mm. Stainless and aluminium cut thinner at the same power because they use nitrogen assist and generate less process heat. Speeds roughly halve for every doubling of thickness at the top of the range.

Maximum thickness by laser power

These figures assume carbon steel with oxygen assist, production-quality cutting. "Maximum" means the machine will get through it; it does not mean the cut is fast, dross-free or economical.

Laser power	Carbon steel (O₂)	Stainless steel (N₂)	Aluminium (N₂)
1 kW	6 – 8 mm	3 – 4 mm	2 – 3 mm
1.5 kW	8 – 10 mm	4 – 5 mm	3 – 4 mm
3 kW	16 – 20 mm	10 – 12 mm	8 – 10 mm
6 kW	20 – 25 mm	16 – 20 mm	12 – 15 mm
12 kW	30 – 40 mm	25 – 30 mm	20 – 25 mm
20 kW	40 – 50 mm	30 – 40 mm	25 – 30 mm

If your work sits within 2–3 mm of these maxima, expect to run slowly, to inspect edges closely, and to spend time on parameter tuning. Most production shops choose a machine rated one step above their thickest routine job.

Indicative cutting speeds

Speeds below are for a well-set-up machine cutting at production quality. Real values depend on the source, the cutting head, gas pressure and nozzle condition, so treat these as planning figures rather than machine settings.

Carbon steel with oxygen assist

Thickness	1 kW	3 kW	6 kW	12 kW
1 mm	8 – 10 m/min	20 – 25 m/min	30 – 40 m/min	45 – 60 m/min
2 mm	4 – 6	12 – 16	22 – 30	35 – 45
3 mm	2.5 – 4	8 – 10	15 – 20	25 – 35
6 mm	1.2 – 1.8	4 – 5	7 – 9	14 – 18
10 mm	—	2.2 – 3	4.5 – 6	9 – 12
12 mm	—	1.8 – 2.2	3.5 – 5	8 – 10
20 mm	—	—	1.6 – 2.2	4 – 5
25 mm	—	—	1.0 – 1.4	2.5 – 3.5

Stainless steel with nitrogen assist

Thickness	1 kW	3 kW	6 kW	12 kW
1 mm	5 – 7 m/min	12 – 18 m/min	20 – 28 m/min	30 – 40 m/min
2 mm	2.5 – 3.5	7 – 10	12 – 18	20 – 28
3 mm	1.5 – 2.2	4 – 6	8 – 12	14 – 20
5 mm	—	2 – 3	4.5 – 6	8 – 12
8 mm	—	1.2 – 1.8	2.5 – 3.5	4.5 – 6
12 mm	—	—	1.3 – 1.8	2.5 – 3.5
20 mm	—	—	—	1.2 – 1.8

Notice that stainless runs at roughly half the carbon steel speed at the same thickness. The reason is process chemistry, not machine quality.

Cutting 40 mm carbon steel: the extreme end of the chart

The speed tables above stop at 25 mm carbon steel and 20 mm stainless, and that limit is deliberate. Beyond it you are at the far end of what fiber laser cutting can do, where speeds collapse and the process demands a different class of machine.

The power table puts 40 mm carbon steel at the top of the 12 kW row, and a 12 kW machine cutting 40 mm is working at its ceiling. In practice you want 12 kW as a floor, and the reward for moving to 20 kW is mostly speed, not new capability. Cutting speed falls to roughly a third of the 25 mm figures in the table above — on the order of 0.5–1.5 m/min depending on power and how clean the edge has to be, where the identical profile in 3 mm sheet would run tens of metres per minute. Piercing gets worse faster than cutting does: the one-second pierces of 12 mm plate become staged routines that can take tens of seconds per hole, so a heavily perforated 40 mm part can spend more of its cycle piercing than cutting.

Edge quality is the other constraint. Expect deeper striations, more dross to remove and noticeably more taper than on thin sheet, and the bottom of the cut can drift far enough off square to matter on mating faces. Nozzle condition, gas pressure and focus control stop being maintenance items at this thickness and become process-critical.

Be honest about the alternatives. Plasma cuts 40 mm carbon steel several times faster at lower consumable cost, trading that for a wider kerf, more edge bevel and a larger heat affected zone. Oxy-fuel reaches the same thickness and well beyond with the cheapest equipment, but cuts slowly and needs the most edge dressing. Fiber laser earns the job when you need narrow kerfs, edges clean enough to use straight off the table, or one machine covering everything from 1 mm to 40 mm. If the work is thick structural plate in volume, with edges that get welded or machined anyway, plasma is usually the more economical answer.

Why the numbers move so much in practice

Six variables explain almost all of the difference between a supplier's demonstration video and your shop floor:

Assist gas and pressure. Oxygen for carbon steel adds exothermic heat and raises speed dramatically. Nitrogen for stainless and aluminium is inert — all the energy comes from the laser. Getting the gas type wrong is the single biggest cause of "the machine won't cut it".
Edge quality requirement. A part that will be painted can be cut faster than one that will be welded or visible. Dross, roughness and taper all improve as you slow down.
Nozzle condition and diameter. A worn or wrong-size nozzle changes gas dynamics at the kerf. This is the cheapest thing to fix and the most commonly neglected.
Focus position. Focus too high gives a wide kerf and dross; too low gives a narrow kerf and poor edge on thick material. Auto-focus heads exist because this matters per material and per thickness.
Material quality. Laser cutting steel from different mills behaves differently. Rusty, oily or heavily scaled sheet cuts slower and produces inconsistent edges.
Nesting and piercing. Speed on the specification sheet is cutting speed. Total cycle time includes piercing — which on 20 mm plate can take several seconds per hole — plus rapid moves and any common-line cutting.

Planning the cut cycle, not just the speed

When you are working out whether a machine can handle your throughput, do not multiply cutting speed by part perimeter. That underestimates the job. Include:

Pierce time. Rises steeply with thickness; a 3 kW machine piercing 12 mm can take over a second per pierce.
Rapid positioning. Fast on a modern machine, but it matters on a part with hundreds of small holes.
Common-line and chain cutting. Nesting software can share cut paths and reduce total travel distance substantially on repeated parts.
Loading and unloading. Often the real bottleneck on a single-table machine; an exchange table addresses it.
Scrap and rework. Thin material distorts; expect a learning curve on thin gauge.

A realistic capacity estimate is usually 50–70% of the theoretical cutting speed, and lower on jobs with heavy piercing or small features.

Choosing power from this table

Work backwards from your routine job, not your thickest one:

Mostly 1–3 mm sheet, high volume → 3 kW to 6 kW. Speed matters more than thickness capability here.
Mixed 3–10 mm fabrication → 6 kW. This is the most common general-purpose choice for a job shop.
Regular 12–25 mm plate → 12 kW. Below this, the process gets slow enough to affect scheduling.
Structural steel, 25 mm and above → 20 kW and above, and look at whether plasma is a better fit for the thickest work.

And remember that the machine is not the only limit: your chiller, extraction, power supply and material handling all have to keep up with the cutting speed you are planning for.

Frequently asked questions

What thickness can a 3kW fiber laser cut?

A 3 kW fiber laser will cut carbon steel to roughly 16-20 mm, stainless steel to about 10-12 mm and aluminium to about 8-10 mm. At the top of those ranges the cut is slow and the edge quality drops, so production work usually stays two or three millimetres below the maximum.

What thickness can a 6kW fiber laser cut?

Around 25 mm carbon steel, 16-20 mm stainless and 12-15 mm aluminium, again with speed and edge quality falling off near the limit.

Does cutting speed halve when thickness doubles?

No, it falls faster than that. Going from 3 mm to 6 mm carbon steel on the same machine typically reduces speed by 50-60%, and from 6 mm to 12 mm by a similar proportion again, because the process moves from high-speed fusion cutting to slower oxidation cutting.

Why is stainless slower to cut than carbon steel?

Stainless is cut with nitrogen rather than oxygen, so there is no exothermic reaction adding heat to the cut. The laser has to supply all the energy, and nitrogen assist is less effective at clearing the kerf, so speeds are typically 40-60% of carbon steel at the same thickness.

Machines mentioned in this article

Fiber Laser Cutting Machine — PL-1390 with Raycus 500W-1kW source
Large Scale Laser Cutting Machine — PL-1625 for large format work
Metal Laser Cutting Machine — CO2 metal cutting in three bed sizes

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