Unified Firmware – Nozzle To Probe Offsets

In order to properly use a bed-leveling probe, the printer’s firmware need to know where the probe is located in relation to the nozzle. This ensures that the printer can place the probe accurately within the boundary of the bed, preventing bad readings and possible damage to the bed, nozzle, and probe.

This procedure is particularly important for touch-based probes such as the BLTouch. If the printer attempts to use the BLTouch outside of the bed’s boundaries, the probe tip may snag on the bed and the nozzle will contact the bed, causing damage to both items. Damage can occur even with touchless sensors such as our EZABL, too, so it is important that these offsets be configured properly.

TH3D’s Unified Firmware provides pre-configured offsets for our EZABL probe mounts, as well as a CUSTOM_PROBE option used for custom mounts or third-party bed-leveling probes.

Measuring Nozzle-to-Probe Offsets #

Initial Measurements #

Use a pair of calipers or a metric ruler to measure the distance between the tip of the nozzle and the tip of the bed-leveling probe. If you are using an EZABL or other touchless sensor with a flat tip, measure to the center of the probe’s tip. For touch-based sensors, measure to the point where the tip extends.

This must be measured in both X and Y dimensions individually. Make sure that you measure the distance both left-to-right (along the X axis) and front-to-back (along the Y axis). Jot these numbers down and make sure you note which measurement is for which axis!

Example measurement taken along the X axis, repeat for the Y axis

Note that we are only using X and Y dimensions here. The Z offset is configured independently via a completely different method and should NOT be configured in this manner.

Positive vs. Negative Values #

Unified Firmware (and Marlin) use positive and negative values to determine the position of the probe relative to the nozzle. There is a diagram within the firmware that acts as a reference. The rules are:

  • The X value must be NEGATIVE if the probe is located to the LEFT of the nozzle, or POSITIVE if it is to the RIGHT of the nozzle.
  • The Y value must be NEGATIVE if the probe is located IN FRONT OF the nozzle, or POSITIVE if it is BEHIND the nozzle.

Unified Firmware Settings #

Unified Firmware’s bed-leveling functions are enabled by selecting either a mount type or the CUSTOM_PROBE option from the section called “EZABL Probe Mounts”.

Example of the EZABL Probe Mounts section in Unified Firmware

EZABL – Mount Types and References #

Our Unified Firmware includes pre-configured offset options for the EZABL. Each version of Unified includes a section with possible EZABL mounts that we provide for those models. If you are using a mount designed by or purchased from TH3D, simply enable the option for your printer/mount.

A full list of TH3D-supported mounts can be found in the configuration_backend.h file of any Unified Firmware version. If you wish to use a mount not included in the main configuration.h file, you can create a new line in the EZABL mount types section for the mount you need.

If you are using a custom or third-party mount that does not match the available options, you will use the CUSTOM_PROBE option.


If you are using a custom or third-party bed-leveling probe or mount, you will enable the CUSTOM_PROBE option from the list of EZABL mount types. Enabling the CUSTOM_PROBE option requires that you configure the NOZZLE_TO_PROBE_OFFSET values manually.

Refer to the first section of this guide to measure your offset values. These values are entered under the explanatory diagram in configuration.h as seen here:

Nozzle-to-Probe offsets are configured below the diagram.

Community Mounts #

Some third-party sensor mounts may have nozzle-to-probe offsets published by the designer. These measurements can usually be trusted, however it may be worth ensuring proper values for any community-created mount. If you have any doubts about the measurements provided, it is always best to measure them yourself to be sure.

Additional Resources #

Video guide by Teaching Tech (Youtube), timestamp beginning 2:53

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