Layer height calculator: nozzle size, line width and magic numbers

Layer height is one of the main 3D printing settings: thinner layers give a finer surface but take longer, thicker ones are faster but show more layer lines. The limit is set by your nozzle diameter. The calculator uses the common rules of thumb:

• layer height: 25–75% of the nozzle; half the nozzle is the balanced choice;
• line width: 100–150% of the nozzle, typically about 112%;
• first layer: half the nozzle, but at least 0.2 mm and no more than 75% of the nozzle.

Nozzle	Layer height	Balanced	Line width (typical)	First layer
0.2 mm	0.05–0.15 mm	0.10 mm	0.20–0.30 mm (0.23)	0.15 mm
0.4 mm	0.10–0.30 mm	0.20 mm	0.40–0.60 mm (0.45)	0.20 mm
0.6 mm	0.15–0.45 mm	0.30 mm	0.60–0.90 mm (0.68)	0.30 mm
0.8 mm	0.20–0.60 mm	0.40 mm	0.80–1.20 mm (0.90)	0.40 mm

Above 75%, a layer isn't pressed into the one below firmly enough, so layer bonding suffers. Below 25%, you rarely see a visible improvement; only the print time grows. A thicker first layer sticks better and is more forgiving of small leveling errors.

A hotend can only melt so much plastic per second. That's its max volumetric flow (mm³/s), and it sets the top speed:

max speed = volumetric flow ÷ (layer height × line width)

The calculator offers starting values for three hotend types: standard (V6-style) about 12 mm³/s, high-flow about 24 mm³/s, Volcano/CHT-style about 35 mm³/s. These are typical for PLA; for PETG and ABS, figure about 20–30% less. If you've measured your own machine, enter your number.

Worked example with a 0.4 mm nozzle, 0.45 mm line width and a 12 mm³/s hotend:

Layer height	Max speed	Time vs. 0.2 mm
0.10 mm	about 267 mm/s	×2.00
0.15 mm	about 178 mm/s	×1.33
0.20 mm	about 133 mm/s	×1.00
0.25 mm	about 107 mm/s	×0.80
0.30 mm	about 89 mm/s	×0.67

Two things stand out. With thin layers the hotend isn't the bottleneck; the machine's motion is. With thick layers you run out of flow fast: at 0.3 mm, a standard hotend may already under-extrude around 90 mm/s. The time factor only counts layers; acceleration and travel moves also affect real print time. Measure your hotend's limit with the flow rate calculator.

On most hobby printers a lead screw driven by a stepper motor moves the Z axis. Each full motor step raises the axis by the same amount:

one step (mm) = lead screw lead ÷ motor steps per revolution

The common T8 screw has an 8 mm lead (four-start), and a 1.8° motor makes 200 steps per revolution. One step is 8 ÷ 200 = 0.04 mm. Layer heights that are whole multiples of that are the "magic numbers": 0.08, 0.12, 0.16, 0.20, 0.24, 0.28 mm and so on.

If a layer height doesn't land on a whole step, say 0.15 mm (3.75 steps), the motor stops on a microstep. Microsteps have less torque and positioning accuracy, so layer heights can vary slightly, which can show up as regular banding (Z banding) on walls. The calculator then gives you the nearest magic value: 0.16 mm instead of 0.15.

More examples:

• 8 mm lead, 0.9° motor (400 steps): one step is 0.02 mm, so 0.10, 0.12, 0.14 … mm are all magic.
• 2 mm lead, 200 steps: one step is 0.01 mm, so practically every common value works.

The calculator lists every magic value within your nozzle's recommended range.

Magic layer heights aren't a cure-all. They matter when:

• your printer has a lead-screw Z axis (most desktop FDM printers do);
• you see regular, evenly spaced horizontal bands on walls and have already ruled out mechanical causes (bent screw, loose coupler).

They matter less when:

• your slicer profiles already use such values (many stock profiles use 0.12, 0.16, 0.20 or 0.28 mm layers, all multiples of 0.04 mm);
• you use variable layer height, where the slicer picks in-between values anyway;
• your Z axis is belt-driven or geared differently. In that case work out the step size from your own drive and enter the Z travel per motor revolution in the lead field.

If you see banding but your layer height is already magic, the 3D print troubleshooting guide covers other causes of Z banding, such as a fluctuating bed temperature.

• Bigger nozzle, faster prints: a 0.6 mm nozzle runs 0.3 mm layers with a 0.68 mm line, laying down far more plastic in the same time. Great for functional parts; the surface is a bit rougher and fine details are lost.
• Smaller nozzle, fine detail: a 0.2 mm nozzle handles 0.05–0.15 mm layers and tiny lettering, but prints take several times longer and the nozzle clogs more easily.
• Line width below the nozzle size: possible, but the plastic doesn't spread properly and parts get weaker, so the calculator starts at 100% of the nozzle.
• First layer: if your bed isn't perfectly flat, a thicker first layer (0.25–0.3 mm) absorbs more of the error.

The calculator gives guideline values based on rules of thumb; a test print always has the final say.