Line width by feature: outer wall, inner wall, top surface, infill and support

On a 0.4 mm nozzle, slicers ship the outer wall at 0.40 to 0.45 mm. Inner walls and infill run as wide as the outer wall or wider, for strength and speed. Top surfaces and supports run as narrow or narrower, for a smoother finish and easier removal.

Line widths by feature for a 0.4 mm nozzle

Feature	Bambu Studio	PrusaSlicer	OrcaSlicer	UltiMaker Cura
First layer	0.50 mm	0.50 mm	0.48 mm (120%)	0.40 mm (100%)
Outer wall	0.42 mm	0.45 mm	0.40 mm (100%)	0.40 mm
Inner walls	0.45 mm	0.45 mm	0.44 mm (110%)	0.40 mm
Top surface	0.42 mm	0.42 mm	0.375 mm (93.75%)	0.40 mm
Sparse infill	0.45 mm	0.45 mm	0.44 mm (110%)	0.40 mm
Internal solid infill	0.42 mm	0.45 mm	0.48 mm (120%)	0.40 mm
Support	0.42 mm	0.40 mm	0.384 mm (96%)	0.40 mm

The profiles behind each column:

• Bambu Studio: the 0.20mm Standard preset. Every Bambu Lab printer’s 0.4 mm nozzle version of it (A1, A1 mini, P1S, X1 Carbon, H2D and the rest) inherits these widths from one base file.
• PrusaSlicer 2.9.6: 0.20mm SPEED @MK4S 0.4. The Original Prusa MK4S STRUCTURAL and 0.15 mm profiles use the same widths.
• OrcaSlicer 2.4.2: the generic printer profiles, which set widths as a percentage of the nozzle.
• UltiMaker Cura 5.13: the built-in defaults, every width equal to the nozzle. Cura’s Creality printer definitions keep these defaults.

The first layer runs wider for bed adhesion: see the first layer line width guide.

In Bambu Studio, PrusaSlicer and OrcaSlicer, a field set to 0 falls back to the Default width. If that is also 0, the slicer uses 1.125 × the nozzle (0.45 mm), or the nozzle size (0.40 mm) for top surfaces and support.

What line width should you use for the outer wall?

Use 0.40 to 0.45 mm on a 0.4 mm nozzle, the range the slicers ship: 0.42 mm in Bambu Studio, 0.45 mm in PrusaSlicer, 0.40 mm in OrcaSlicer’s generic profiles and UltiMaker Cura. Keep the outer wall equal to or narrower than the inner walls, because a thinner outer line prints finer detail.

The slicer makers give their reasons in the setting descriptions:

• UltiMaker Cura, Outer Wall Line Width: “By lowering this value, higher levels of detail can be printed.”
• PrusaSlicer, Perimeters: “You may want to use thinner extrudates to get more accurate surfaces.”
• OrcaSlicer wiki: the outer wall “controls dimensional accuracy and surface finish.” It recommends 105% to 120% of the nozzle (0.42 to 0.48 mm) “for clean overhangs and detail,” wider than the 100% its own generic profiles ship.

A narrower outer line also makes the wall thinner. At 0.2 mm layers, Bambu Studio’s 0.42 mm outer wall and one 0.45 mm inner wall make a 0.827 mm wall, and PrusaSlicer’s two 0.45 mm walls make 0.857 mm. Neighboring lines overlap slightly, so the total comes in under the plain sum. Enter your own widths in the line width calculator.

These widths hold exactly only with the Classic wall generator. The OrcaSlicer wiki notes that Arachne, the variable-width generator, adjusts each line to the model’s geometry and treats the set values as a reference.

Inner wall and infill line width

Inner walls and sparse infill are where slicers go wide: 0.44 to 0.45 mm on a 0.4 mm nozzle in Bambu Studio, PrusaSlicer and OrcaSlicer. PrusaSlicer’s Infill tooltip says to use “fatter extrudates to speed up the infill and make your parts stronger.”

The OrcaSlicer wiki gives a target for each:

Feature	OrcaSlicer wiki	0.4 mm nozzle	Why
Inner wall	120% or more	0.48 mm or more	Wider than the outer wall “to enhance structural strength”
Sparse infill	about 115%	0.46 mm	Layer adhesion “without getting near volumetric flow limitations”
Internal solid infill	about 110%	0.44 mm	“Good layer adhesion and visual quality”

For stronger infill, the wiki suggests the infill line multiplier instead of a wider line.

A wider line carries more plastic, so it hits the filament’s flow limit at a lower speed. Bambu Studio’s generic PLA profile allows 12 mm³/s. At 0.2 mm layers a 0.45 mm line tops out at about 147 mm/s and a 0.40 mm line at about 168 mm/s. Each line’s cross-section is a rectangle with rounded sides, as the slicers model it: 0.2 × (0.45 − 0.2 × (1 − π/4)) = 0.0814 mm², and 12 ÷ 0.0814 = 147. Check your own filament and speeds with the volumetric flow calculator.

What line width should you use for top surfaces?

Use about the nozzle size, 0.375 to 0.42 mm on a 0.4 mm nozzle, and no wider than the outer wall. Bambu Studio and PrusaSlicer ship 0.42 mm, UltiMaker Cura 0.40 mm and OrcaSlicer’s generic profiles 0.375 mm. PrusaSlicer’s tooltip says thinner top lines fill narrow regions and give a smoother finish.

Prusa’s 0.10mm FAST DETAIL @MK4S 0.4 profile drops the top surface to 0.40 mm. The OrcaSlicer wiki recommends 100% to 105% of the nozzle (0.40 to 0.42 mm) “for smooth results without over-extrusion.”

The top surface (Bambu Lab’s wiki calls it the top layer) is only the uppermost skin. The solid layers under it print at the internal solid infill width.

In UltiMaker Cura, Top/Bottom Line Width covers every top and bottom skin layer. For a separate width on the top surface, set Top/Bottom → Top Surface Skin Layers to 1 or more (the default is 0), then set Top Surface Skin Line Width.

What line width should you use for supports?

Use about the nozzle size, 0.384 to 0.42 mm on a 0.4 mm nozzle. PrusaSlicer and UltiMaker Cura ship 0.40 mm, Bambu Studio 0.42 mm and OrcaSlicer’s generic profiles 0.384 mm. Go below the nozzle if supports are hard to remove, and back to 100% if they break during the print or leave debris.

The Prusa Knowledge Base says a width under the nozzle makes supports “weaker and easier to remove.” The OrcaSlicer wiki calls 100% typical and warns that supports printed too narrow can break and leave debris on the model.

Bambu Studio’s Support width also covers the support interface. Cura sets the interface separately, under Support Interface Line Width (0.40 mm by default). In PrusaSlicer, the Support material width unlocks only once Generate support material is on.

How to change line width in each slicer

Feature	Bambu Studio	PrusaSlicer	OrcaSlicer	UltiMaker Cura
Where	Process → Quality → Line width	Print Settings → Advanced → Extrusion width	Process → Quality → Line width	Print settings → Quality → Line Width
Outer wall	Outer wall	External perimeters	Outer wall	Outer Wall Line Width
Inner walls	Inner wall	Perimeters	Inner wall	Inner Wall(s) Line Width
Top surface	Top surface	Top solid infill	Top surface	Top Surface Skin Line Width (under Top/Bottom)
Sparse infill	Sparse infill	Infill	Sparse infill	Infill Line Width
Internal solid infill	Internal solid infill	Solid infill	Internal solid infill	Top/Bottom Line Width
Support	Support	Support material	Support	Support Line Width
Units	mm	mm, or % of the layer height	mm, or % of the nozzle	mm

The line width fields are Advanced-mode settings in Bambu Studio, PrusaSlicer and OrcaSlicer. If they are hidden, switch the settings view to Advanced. In Cura, Support Line Width and the Top Surface Skin settings show only with settings visibility set to Expert.

Type widths in millimeters in PrusaSlicer. Its percentages are taken of the layer height, so a 0.45 mm line at 0.2 mm layers is 225%. OrcaSlicer reads percentages from the nozzle: 112.5% is 0.45 mm on a 0.4 mm nozzle, and the width scales when you change nozzles.

The slicer works out the plastic in each line from its width and layer height, so the extrusion follows any new width. Bambu Lab’s wiki advises keeping the default widths and, if you change them, staying within 0.75 to 1.5 × the nozzle (0.30 to 0.60 mm on a 0.4 mm nozzle). The line width calculator lists each slicer’s hard limits.