Choosing a Layer Height

What layer height actually changes

Layer height is the thickness of each slice the printer builds, measured in the Z direction. It does not change how fine the printer can draw within a layer (that is the nozzle width on FDM, or the pixel or laser spot size on resin). It changes four things:

• Detail on slopes and curves. A sloped or curved surface is built as a stack of flat steps. Each step is one layer tall, so thinner layers mean smaller steps and a smoother surface. Vertical walls and flat tops look much the same at any layer height.
• Print time. The printer traces every layer, so halving the layer height roughly doubles the number of layers. Polymaker notes that a 0.1 mm layer height triples print time compared with 0.3 mm at the same nozzle and speeds Rule of thumb.
• Layer bonding on FDM. Each new line has to be pressed into the one below. Prusa warns that going past the maximum (see below) significantly compromises layer adhesion.
• Chances to fail. More layers mean more repetitions of every move. Formlabs makes the same point for resin: more layers give more opportunities for something to go wrong.

Where stair-stepping shows most

Stair-stepping is worst on surfaces that are close to flat but not quite: a shallow dome, a gently sloped roof, the low areas of a relief. On a steep slope each layer moves the edge only a little sideways, so the steps are small. On a shallow slope each layer moves the edge a long way, so each step becomes a visible terrace. Formlabs lists organic forms, rounded arches, small embossing and intricate engraving as the shapes that gain most from finer Z resolution, and says models made mostly of flat faces and right angles gain little.

FDM: the nozzle rule of thumb

Rule of thumb A commonly cited working range for FDM layer height is about 25 to 75 percent of the nozzle diameter. Polymaker gives that range and notes that some suggest 20 to 80 percent. At the top end, Prusa's nozzle guide says layer height should be 70 to 80 percent of the nozzle diameter at most, and that a layer taller than the nozzle cannot be printed at all.

Why the nozzle sets the limit: the flat tip of the nozzle presses each line down onto the layer below. If the layer is nearly as tall as the nozzle opening, there is little squish and the bond between layers suffers. Far below the range, the printer spends a very long time drawing tiny steps, for little visible gain on most surfaces.

Nozzle	25 to 75 percent range Rule of thumb
0.25 mm	about 0.06 to 0.19 mm
0.4 mm	about 0.10 to 0.30 mm
0.6 mm	about 0.15 to 0.45 mm
0.8 mm	about 0.20 to 0.60 mm

These are arithmetic on the rule of thumb, not settings. Your slicer's built-in profiles for your printer and nozzle are tuned starting points Starting point; pick the one closest to what you want and change from there.

Picking a value

• Functional parts, prototypes, big boxes: toward the thick end. Mostly vertical walls do not benefit from thin layers, and you save hours.
• Figures, curved shells, lettering on top surfaces: toward the thin end, or use variable layer height so only the curved parts slow down.
• Reliefs printed flat: the whole design lives in a few millimeters of height and is mostly gentle slopes, which is exactly where stair-stepping shows. See Printing a CNC Relief STL.

The first layer is its own setting

Most slicers let you set a separate first layer height. Polymaker notes that the initial layer height prioritizes adhesion over detail, which is why profiles often use a first layer slightly thicker than the rest. If your first layer is not sticking, layer height is rarely the cause; see First Layer Won't Stick.

Counting layers

The calculator below does this for you. Layer count is a better guide to time than layer height alone, because time scales with how many layers there are.

Resin layer heights

On resin printers, the light cures one thin layer at a time, and the exposure time in the resin profile is matched to a particular layer height. That is why resin profiles are usually set up for specific layer heights, and why changing the layer height usually means changing the exposure too. Formlabs says its printers support layer thicknesses between 25 and 300 microns depending on the material Maker spec. Hobby MSLA slicers and resin makers publish their own profiles; use a layer height for which your resin maker gives an exposure setting, or run the maker's exposure test when you change it.

The trade-offs are the same as FDM. Formlabs notes that printing at 25 microns instead of 100 usually takes about four times as long Rule of thumb, and that the gain is largest on organic, curved and finely engraved shapes. Resin already shows far less stair-stepping than FDM at typical settings, so a thinner layer is often not worth the time on parts made of flat faces.

Variable and adaptive layer height

A single model rarely needs the same layer height everywhere. A figure might need fine layers on the face and shoulders and nothing special on the straight legs of its stand. Variable layer height lets the slicer use thin layers only where the surface is shallow or curved.

PrusaSlicer's variable layer height tool, as Prusa documents it, offers three ways to do this:

• Adaptive: calculates a layer profile from the model's shape, with a quality versus speed slider.
• Smooth: evens out the profile so layer height does not jump abruptly, with an option to keep the smallest layers.
• Manual editing: drag over areas of the model to add or remove detail by hand.

Other slicers have similar features under names like adaptive layer height; check your slicer's documentation for where it lives. Adaptive layers are most useful on models with a mix of steep and shallow surfaces, such as domes, figures and reliefs.

A sensible way to decide

1. Start with your slicer's standard profile for your printer and nozzle Starting point.
2. Look at the model. Mostly vertical walls and flat tops: go thicker. Shallow curves and fine top-surface detail: go thinner, or use variable layer height.
3. Check the layer count and the slicer's time estimate before committing.
4. If you are unsure, print a small section of the model at two layer heights and compare them in raking light.