Line width is one of the more confusing settings in any slicer because it sounds like it should just match your nozzle diameter, yet every major slicer defaults to a value that’s slightly wider. The setting is closely tied to nozzle size, which we cover in depth in our nozzle size guide, but line width has its own effects on strength, speed and detail that are worth understanding on their own.
What line width actually measures
Line width is the width of the bead of plastic the nozzle lays down, not the diameter of the nozzle opening itself and not the same thing as flow rate or extrusion multiplier. CNC Kitchen draws a useful distinction on this exact point: extrusion multiplier changes how much material comes out while keeping the spacing between lines the same, while line width changes the spacing between lines and lets the slicer adjust flow to match. Mixing the two up is an easy way to end up with either stringy under-extrusion or blobby over-extrusion while chasing the wrong setting.
Why slicers default above 100 percent
The nozzle diameter is fixed, but the bead it produces isn’t, since the molten plastic gets squeezed and flattened against the bed or the layer below rather than staying round. Bambu Lab’s documentation explains the mechanics: increasing extrusion flow relative to nozzle travel speed pushes out more material, and that surplus gets flattened wider by the nozzle’s tip, up to the point where it reaches the nozzle’s outer flat area. OrcaSlicer’s own guidance backs this up from a print-quality angle: line width below 100 percent risks poor adhesion between lines, while pushing past roughly 150 percent risks visible over-extrusion, blobbing and rough surfaces. In between, wider lines get squeezed harder into the layer below, which tends to improve layer bonding, not just line-to-line adhesion.
What the major slicers default to
PrusaSlicer’s default sits close to 120 percent of nozzle diameter, while Cura defaults nearer 100 percent, and CNC Kitchen’s own summary of slicer behavior across the board lands on a 100 to 120 percent range as typical. If you want to experiment beyond the defaults, both Bambu Lab’s documentation and CNC Kitchen’s write-up converge on the same outer bound: somewhere between 0.75 and 1.5 times the nozzle diameter is the range where quality holds up before either poor adhesion or over-extrusion problems start to show. Changing the nozzle itself, not just the line width percentage, is a bigger lever for wall thickness and print speed; see 0.4mm vs 0.6mm nozzle for that tradeoff.
What testing shows about strength and quality
CNC Kitchen ran extrusion widths from 90 percent up to 250 percent on a 0.4 mm nozzle (0.36 mm to 1 mm) and tracked both print quality and layer adhesion strength. Quality held up almost identically from 90 percent through about 140 percent, with the first visible artifacts appearing around 160 percent and clear surface texture problems by 250 percent. Layer adhesion strength climbed steadily from 90 percent up to a peak somewhere around 150 percent, then fell off as the extra material started causing its own defects. In a separate test using load-bearing hooks, two walls printed at double width beat four walls at standard width on break strength, while also finishing faster, since fewer wall loops had to be traced per layer. None of that means maxing out line width is free. Thin or highly detailed features still need a wall count that can trace their shape properly.
Line width, flow limits and speed
A wider line means more plastic has to move through the nozzle per second at any given print speed, and that pushes closer to the hotend’s maximum volumetric flow rate, the same limit that becomes the bottleneck on larger nozzles as covered in our nozzle size guide. If a print starts under-extruding only at higher speeds after you’ve widened your lines, that ceiling is a likely cause, and the fix is usually to slow down rather than change temperature. Our PLA print settings guide has more on how speed and flow interact if you’re chasing print time reductions on top of a wider line width.
Setting different widths per feature
Modern slicers like OrcaSlicer don’t force one line width across the whole print. Its documentation lists separate recommended ranges by feature: outer walls at 105 to 120 percent for a clean surface, inner walls at 120 percent or more since they’re hidden and can be pushed harder for strength, top surfaces closer to 100 to 105 percent to avoid over-extrusion on visible flat areas, and sparse infill around 115 percent as a middle ground between strength and flow limits. Splitting these out rather than using one blanket value across the whole print lets you push strength where it matters and keep finish quality where it’s visible.
Checklist
- Line width is the width of the extruded bead, not the nozzle bore diameter and not the same thing as flow percentage.
- Most slicers default to 100 to 120 percent of nozzle diameter, wide enough to squeeze the bead flat for good adhesion.
- A safe range to experiment in is roughly 0.75 to 1.5 times the nozzle diameter before quality or adhesion suffers.
- Wider lines generally test stronger for layer bonding up to a point, then quality drops off past about 150 to 160 percent.
- Wider lines need more plastic per second at a given speed, which can hit your hotend’s maximum volumetric flow before its rated speed does.
- Set outer walls, inner walls, top surfaces and infill separately where your slicer allows it, rather than using one width everywhere.