# LinuxCNC G90.1

Instructions · `G90.1` · verification: source checked

G90.1 selects absolute arc distance mode in LinuxCNC, so the I, J and K arc center offsets in G2/G3 blocks are measured as absolute distances from the current 0 position of the axis rather than from the arc start point. In this mode both offsets for the active plane must be programmed: I and J for the XY plane, or J and K for the XZ plane. Incremental offsets, which are the default, are restored with G91.1.

## Specification

| Property | Value |
|---|---|
| Language | gcode |
| Code | G90.1 |
| Group | Arc Distance Mode |
| Syntax | G90.1 |
| Dialect | LinuxCNC |

## Connected

- Related: [LinuxCNC G02](https://machineschema.com/instruction/gcode-g02.md)

## Safety

- Programming G90.1 without both required offsets for the active plane (I and J in the XY plane, J and K in the XZ plane) with G2/G3 is an error.

## Study notes

- Arc center offsets in absolute arc distance mode are the absolute distance from the current 0 position of the axis.
- For arcs of less than 360 degrees, one or more axis words and both offsets must be programmed.
- For full circles, no axis words and both offsets must be programmed; the P word defaults to 1 and is optional.
- Incremental arc distance mode (G91.1) is the default; G91.1 returns I, J and K to their default behavior.
- Center format arcs using I, J and K offsets are more accurate than radius format arcs and are the preferred format.

## Sources

1. [G-Codes](https://linuxcnc.org/docs/html/gcode/g-code.html#gcode:g90.1-g91.1) (accessed 2026-10-26)

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Source page: https://machineschema.com/instruction/gcode-g90-1  
JSON: https://machineschema.com/instruction/gcode-g90-1.json  
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite Machine Schema and the original sources.