Z Offset: Setting the Right Nozzle-to-Bed Distance

Even with a perfectly level bed, the first layer goes wrong if the nozzle is a few hundredths of a millimeter too far or too close. Z offset is the value you set to adjust that last small difference. On printers with an auto bed leveling sensor this setting is required, because the sensor measures the bed but does not know how far below the sensor the nozzle sits.

Why do you need Z offset?

• On printers with a sensor: A BLTouch, CR Touch or inductive sensor sits next to the nozzle, a little above it. When the sensor touches the bed, the nozzle is still in the air. Z offset compensates for this height difference.
• On printers without a sensor: The position of the Z axis limit switch or the bed adjustment knobs does this job. You can still use the firmware's Z offset or babystep for fine adjustment.
• After changing the nozzle: A new nozzle may be slightly different in length from the previous one.

Understand the sign

The Z offset value can be negative or positive. The rule is simple:

• As the value gets smaller (more negative, for example from −1.50 to −1.60), the nozzle moves closer to the bed.
• As the value gets bigger (for example from −1.60 to −1.50), the nozzle moves away from the bed.

On most printers with a sensor the value is a negative number between −0.5 and −3.0 mm.

What does the right distance look like?

Look at the lines while the first layer prints:

Method 1: rough setting with paper

1. Heat the bed and nozzle to printing temperature.
2. Home the printer.
3. Bring the nozzle to the middle of the bed and lower Z to 0.
4. Put paper between the nozzle and bed and adjust the value in the screen's Z offset menu in steps of 0.05 mm until you feel slight drag.
5. Save the value.

Because paper is about 0.1 mm thick, this method only gives a rough start. Do the fine adjustment during a print.

Method 2: fine adjustment during the print (babystep)

The most accurate method.

1. Print a single-layer test model that covers a large part of the bed (for example a 50 × 50 mm square or a pattern across the bed).
2. While the first layer prints, open the Z offset or babystep option in the screen's "Tune" menu.
3. Change the value in steps of 0.01–0.02 mm. After each change wait a few seconds and watch how the lines change.
4. Stop when the lines flatten and fuse together.
5. Save the value. In Marlin, the babystep value may need the M500 command to be saved. Some interfaces do this automatically.

Method 3: setting with commands (Marlin)

• M851 shows the current probe Z offset value.
• M851 Z-1.62 sets a new value.
• M500 saves it to permanent memory.

In Klipper the PROBE_CALIBRATE command determines the probe offset with the paper test. During a print you fine-tune with SET_GCODE_OFFSET Z_ADJUST=-0.02 and save with Z_OFFSET_APPLY_PROBE and SAVE_CONFIG.

For different surfaces

If you use build plates of different thickness (for example smooth PEI and textured PEI), the thickness difference affects the Z offset. Note a separate value for each plate, or add an offset to the start G-code based on plate type in the slicer.

The difference between Z offset and bed level

• Bed level makes every point of the bed the same distance from the nozzle. See Bed leveling.
• Z offset sets that shared distance itself.

If the level is right, the whole bed prints the same way; Z offset makes that "same way" correct. If one side of the bed is good and the other bad, the problem is the level, not the Z offset.

Frequently asked questions

The Z offset changes every print. Why?

The sensor mount may be loose, the sensor tip may be dirty or the sensor may be sensitive to temperature. A bed or nozzle change also causes differences. Check the sensor mounting screws and how tight the nozzle is.

The Z offset is right but the first layer is still bad?

The bed may not be clean, the temperature may be low or the first layer speed may be high. See First layer not sticking.