Guide

G-code Format: The Complete Guide for 3D Printing and CNC

PC By Pablo Cirre • Updated May 7, 2026

What Is G-code?

G-code (also called RS-274 or CNC code) is the programming language used to control CNC (Computer Numerical Control) machines — including 3D printers, CNC milling machines, lathes, plasma cutters, laser engravers, and pick-and-place machines. It originated at MIT in the 1950s and was standardized as RS-274 by the Electronic Industries Alliance (EIA). The ISO version is ISO 6983.

For 3D printing specifically, G-code is the output of slicers (software that converts 3D models to print instructions): Cura, PrusaSlicer, Bambu Studio, Simplify3D, SuperSlicer. Every FDM (Fused Deposition Modeling) 3D printer reads G-code; laser cutters and CNC routers use dialect variants.

A G-code file is plain text — every line is either a command, a comment (enclosed in ;), or blank. Commands consist of a letter code followed by a number, with optional parameters.

G-code File Structure

; Generated by Cura 5.6.0
; Layer count: 142
; Filament used: 4.82m
; Print time: 2h 15min

M104 S215 ; Set extruder temperature to 215°C (no wait)
M109 S215 ; Set extruder temp and wait for it to reach target
M140 S60  ; Set bed temperature to 60°C (no wait)
M190 S60  ; Set bed temp and wait

G28       ; Home all axes (X, Y, Z to endstops)
G29       ; Auto bed leveling (if supported)
G1 Z5 F5000   ; Move Z to 5mm
G21           ; Set units to millimeters
G90           ; Absolute positioning mode
M82           ; Extruder absolute mode
G92 E0        ; Reset extruder position to 0

; === Start of actual print ===
G0 F9000 X50 Y50 Z0.2     ; Rapid move to start position, Z=0.2mm (first layer height)
G1 F1200 X100 Y50 E5.0    ; Feed move: print line to X100, extruding 5mm of filament
G1 F1200 X100 Y100 E10.0  ; Continue printing
; ... thousands more lines ...

M104 S0  ; Extruder off
M140 S0  ; Bed off
G91      ; Relative positioning
G1 Z10   ; Raise Z by 10mm
G90      ; Back to absolute
G1 X0 Y200 ; Move print head to front
M84      ; Disable motors

G-code Command Types

G Commands (Preparatory Functions)

Command	Description
`G0`	Rapid move (no extrusion, maximum speed)
`G1`	Linear move (coordinated axes + optional extrusion)
`G2`	Clockwise arc move
`G3`	Counter-clockwise arc move
`G4 P500`	Dwell (pause 500 ms)
`G20`	Units: inches
`G21`	Units: millimeters
`G28`	Home axes (to endstops)
`G29`	Auto bed leveling (mesh probing)
`G90`	Absolute positioning
`G91`	Relative positioning
`G92 E0`	Set current position as origin (reset E)

M Commands (Miscellaneous)

Command	Description
`M0`	Stop program (pause, wait for user)
`M82`	Extruder: absolute mode
`M83`	Extruder: relative mode
`M84`	Disable stepper motors
`M104 S215`	Set extruder temperature (no wait)
`M109 S215`	Set extruder temperature and wait
`M140 S60`	Set heated bed temperature (no wait)
`M190 S60`	Set heated bed temperature and wait
`M106 S128`	Set fan speed (0–255, here ~50%)
`M107`	Fan off
`M117 Hello`	Display message on LCD
`M600`	Filament change (pause, retract, wait)
`M900 K0.05`	Linear advance factor

Parameter Letters

Letter	Meaning
`X`, `Y`, `Z`	Axis coordinates (mm or inches)
`E`	Extruder position (mm of filament to push/retract)
`F`	Feed rate (mm/min)
`S`	Spindle speed / temperature / value
`P`	Time (ms) or parameter
`I`, `J`	Arc center offsets (for G2/G3)
`R`	Arc radius

Coordinate Systems

Absolute vs Relative Mode

Absolute (G90): All coordinates are from machine home (0,0,0). G1 X50 moves to 50mm from origin.
Relative (G91): All coordinates are relative to current position. G1 X10 moves 10mm in X direction from wherever the head is now.

Most slicers use absolute for XYZ and relative for E (extruder), or absolute for everything after G92 E0 (reset).

Coordinate Origin and Build Volume

The origin is typically the front-left corner of the print bed at Z=0 (bed surface). The build volume is defined in firmware: a Bambu Lab X1C has 256×256×256mm, a Creality Ender 3 has 220×220×250mm.

FDM 3D Printing Specific G-code

Extrusion Calculation

The E value controls how much filament is pushed through the extruder. In absolute mode, E accumulates across the print:

G1 X100 Y50 E5.2 F1200   ; Move to (100,50), extrude to E=5.2mm total
G1 X150 Y50 E8.7 F1200   ; Continue to (150,50), extrude to E=8.7mm total (3.5mm more)

Filament volume formula:

Volume (mm³) = π × (filament_diameter/2)² × E_distance
For 1.75mm filament: Volume = π × 0.875² × E ≈ 2.405 × E mm³

Retraction

Retraction pulls filament back before non-print moves to prevent stringing:

G1 E-4.5 F3600  ; Retract 4.5mm at 60mm/s (rapid retract)
G0 X80 Y80      ; Rapid travel move
G1 E0 F3600     ; Prime (push back) 4.5mm before next extrusion

Layer Changes

; Layer 12
;LAYER:12
G0 F9000 X44.5 Y44.5 Z1.4  ; Move to new layer height Z=1.4mm (layer 12 × 0.12mm layer height + first layer)

Slicers and G-code Generation

Slicers convert STL/3MF/OBJ files to G-code:

Slicer	Supports	Notable Features
Ultimaker Cura	FDM (most brands)	Plugin ecosystem, profile library
PrusaSlicer	FDM, SLA (Prusa, generic)	Multi-material, paint-on supports
Bambu Studio	Bambu Lab printers	AMS multi-color, AI supports
Simplify3D	FDM (commercial)	Fine control, multi-process
OrcaSlicer	FDM (generic)	Calibration tools, advanced settings
LightBurn	Laser cutters	Vector/raster laser paths
Fusion 360 CAM	CNC machining	Professional toolpath generation

STL to G-code workflow

STL/3MF file → Slicer → G-code → USB/SD card/WiFi → Printer → Physical part

Key slicer settings that affect G-code:

Layer height: Resolution (0.1–0.4mm typical)
Print speed: Line/travel speed (30–300 mm/s)
Infill: Internal structure density and pattern
Support structures: For overhangs beyond 45°
Temperature profile: Per-material extruder and bed temps
Retraction: Distance and speed to prevent stringing

Inspecting and Editing G-code

Text editors

G-code is plain text — any text editor works. VSCode has G-code syntax highlighting extensions.

# View first 30 lines of G-code
head -30 print.gcode

# Count layers
grep -c "^;LAYER:" print.gcode

# Extract all temperatures set
grep "^M109\|^M104" print.gcode

# Find layer 50
grep -n "LAYER:50" print.gcode

G-code simulators / visualizers

Repetier-Host: Desktop G-code host + visualizer
Pronterface (Printrun): G-code sender with 2D preview
gCodeViewer.com: Online 3D G-code visualizer
NCViewer.com: Online CNC G-code viewer

G-code Dialects

Different firmware and machines use different G-code dialects:

Dialect	Used By
Marlin	Most open-source FDM printers (Ender, Prusa original)
Klipper	High-speed printers (Voron, Bambu architecture)
RepRap G-code	Original RepRap specification
Fanuc G-code	Industrial CNC machines
Grbl	Hobbyist CNC routers, laser engravers
LinuxCNC	Open-source industrial CNC
Smoothieware	Smoothieboard controllers

Klipper uses macros in printer.cfg and passes G-code through Python for advanced motion planning. Marlin handles commands directly in firmware. A G-code file valid for Marlin may need modification for Klipper.

Converting STL to G-code

# CuraEngine command-line (Cura's slicer engine)
CuraEngine slice -j printer_profile.json -l model.stl -o output.gcode

# PrusaSlicer command-line
prusa-slicer --slice --load config.ini model.stl --output output.gcode

# Inspect the result
wc -l output.gcode  # count lines (a complex print = millions of lines)

G-code's plain-text format, its 70-year lineage, and its universality across industries from dental implants to automotive prototyping to aerospace tooling — all from the same fundamental command set — makes it one of the most durable technical formats in manufacturing history.

Related conversions

Frequent conversions across the catalogue:

Frequently Asked Questions

G0 is a rapid move — the machine moves as fast as possible (maximum feed rate) with no material output. Used for travel moves between features. G1 is a coordinated linear move at a specified feed rate (F parameter), used for actual cutting or printing where motion speed affects quality. In 3D printing, G0 moves the print head over areas already printed (no extrusion), while G1 moves it while extruding filament to build the part.

G0 is a rapid move — the machine moves as fast as possible (maximum feed rate) com no material output. Used para travel moves between features. G1 is a coordinated linear move at a specified feed rate (F parameter), used para actual cutting ou printing where motion speed affects quality. In 3D printing, G0 moves the print head over areas already printed (no extrusion), while G1 moves it while extruding filament to build the part.

G0 is a rapid move — the machine moves as fast as possible (maximum feed rate) mit no material output. Used für travel moves between features. G1 is a coordinated linear move at a specified feed rate (F parameter), used für actual cutting oder printing where motion speed affects quality. In 3D printing, G0 moves the print head over areas already printed (no extrusion), while G1 moves it while extruding filament to build the part.

G0 is a rapid move — the machine moves as fast as possible (maximum feed rate) con no material output. Used para travel moves between features. G1 is a coordinated linear move at a specified feed rate (F parameter), used para actual cutting o printing where motion speed affects quality. In 3D printing, G0 moves the print head over areas already printed (no extrusion), while G1 moves it while extruding filament to build the part.

On KaijuConverter every file is processed inside an isolated container, encrypted in transit (TLS 1.3) and at rest, and automatically deleted after 60 minutes with multi-pass overwrite. We never train on, share, or analyze user content. For maximum privacy on extremely sensitive material, prefer offline tools (ImageMagick, FFmpeg, LibreOffice) that you control end-to-end.

You need a slicer: open the STL file in Cura, PrusaSlicer, or Bambu Studio. Configure your printer profile (bed size, nozzle diameter), material settings (temperature, retraction), and print quality settings (layer height, speed, infill). The slicer then generates G-code automatically. For command-line use: `CuraEngine slice -j printer.json -l model.stl -o output.gcode` or `prusa-slicer --slice model.stl`. The resulting .gcode file transfers to the printer via SD card, USB, or WiFi.

You need a slicer: abrir the STL arquivo in Cura, PrusaSlicer, ou Bambu Studio. Configure your printer profile (bed size, nozzle diameter), material settings (temperature, retraction), e print quality settings (layer height, speed, infill). The slicer then generates G-code automatically. para command-line use: `CuraEngine slice -j printer.json -l model.stl -o output.gcode` ou `prusa-slicer --slice model.stl`. The resulting .gcode arquivo transfers para o printer via SD card, USB, ou WiFi.

You need a slicer: öffnen the STL Datei in Cura, PrusaSlicer, oder Bambu Studio. Configure your printer profile (bed size, nozzle diameter), material settings (temperature, retraction), und print quality settings (layer height, speed, infill). The slicer then generates G-code automatically. für command-line use: `CuraEngine slice -j printer.json -l model.stl -o output.gcode` oder `prusa-slicer --slice model.stl`. The resulting .gcode Datei transfers zum printer via SD card, USB, oder WiFi.

You need a slicer: abrir the STL archivo in Cura, PrusaSlicer, o Bambu Studio. Configure your printer profile (bed size, nozzle diameter), material settings (temperature, retraction), y print quality settings (layer height, speed, infill). The slicer then generates G-code automatically. para command-line use: `CuraEngine slice -j printer.json -l model.stl -o output.gcode` o `prusa-slicer --slice model.stl`. The resulting .gcode archivo transfers al printer via SD card, USB, o WiFi.

For 95% of use cases, yes — server-side ImageMagick, FFmpeg and LibreOffice produce identical output to the same tools on your laptop. Desktop software wins for: extremely large files (multi-GB), batch jobs of thousands of files, scripted pipelines, or content too sensitive to upload. KaijuConverter caps at 25 MB per file on the free tier (up to 2 GB on paid plans).

Yes, G-code is plain text and can be edited in any text editor. Common edits: changing temperature in M104/M109 lines, adjusting fan speed (M106 values), modifying first-layer height (Z value in initial G1 commands), or fixing specific retraction values. For systematic changes across the entire print, use search-and-replace. However, complex changes like layer reorganization or path optimization are better handled by re-slicing with different slicer settings.

Sim, G-code is plain text e can be edited in any text editor. Common edits: changing temperature in M104/M109 lines, adjusting fan speed (M106 values), modifying first-layer height (Z value in initial G1 commands), ou fixing specific retraction values. para systematic changes across the entire print, usar search-and-replace. Porém, complexo changes like layer reorganization ou path optimization are better handled by re-slicing com different slicer settings.

Ja, G-code is plain text und can be edited in any text editor. Common edits: changing temperature in M104/M109 lines, adjusting fan speed (M106 values), modifying first-layer height (Z value in initial G1 commands), oder fixing specific retraction values. für systematic changes across the entire print, verwenden search-and-replace. Jedoch, complex changes like layer reorganization oder path optimization are better handled by re-slicing mit different slicer settings.

Most format conversions are lossy by design — JPG, MP3, MP4, WebP all discard perceptual data to save bytes. Going through a lossy intermediate compounds the loss. To minimize visible/audible drift: convert from the original master, choose a higher quality setting, and avoid converting back and forth between lossy formats.

Different firmware supports different command subsets. Marlin, Klipper, RepRap, and Grbl each implement different commands. A G29 (auto bed leveling) command works on printers with the feature enabled; printers without a BLTouch or mesh leveling probe will ignore it or error. Check your printer firmware version and documentation for supported commands. Klipper especially has different macro syntax and ignores non-standard M-codes that Marlin supports.

Yes — KaijuConverter accepts multiple files in a single drop and returns a ZIP. For very large batches (thousands of files) consider command-line tools or our API: <code>find . -name "*.heic" -exec magick {} {.}.jpg \;</code> or similar one-liners scale to millions of files when run locally.