G-Code & M-Code Reference: Complete CNC Programming Commands with Real Examples (2025)

Meta Description: Master CNC programming with this ultimate G-code and M-code reference guide. Includes command explanations, usage tips, real machining examples, and charts you can use directly in your shop.

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🔍 What is G-Code?

G-code (Geometric Code) is the language that CNC machines use to control movements such as positioning, cutting, drilling, and more. Each command begins with a “G” followed by a number. Example: G01 = linear feed motion.

🧠 What is M-Code?

M-code (Machine Code) performs machine-level operations like turning the spindle on/off, changing tools, or coolant control. These are essential for managing the state of the machine. Example: M03 = spindle on clockwise.

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📘 Essential G-Codes and Their Functions

G-Code	Function	Example
G00	Rapid Positioning	G00 X100 Y50 – moves tool quickly to position
G01	Linear Interpolation	G01 X100 Y50 F200 – move at feedrate
G02 / G03	Circular Interpolation (CW/CCW)	G02 X100 Y50 I20 J0 – clockwise arc
G17 / G18 / G19	Plane Selection (XY/XZ/YZ)	G18 – switch to XZ plane
G20 / G21	Unit Selection (inch/mm)	G21 – set units to millimeters
G28	Return to Home	G28 U0 V0
G40	Cutter Radius Compensation Cancel	G40
G43	Tool Length Compensation +	G43 H01
G90 / G91	Absolute / Incremental Positioning	G90 = absolute, G91 = incremental
G94	Feedrate per Minute	G94 F300

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📘 Essential M-Codes and Their Functions

M-Code	Function	Example
M00	Program Stop	M00 – operator intervention required
M03 / M04	Spindle On CW / CCW	M03 S1200 – start spindle at 1200 RPM CW
M05	Spindle Stop	M05
M06	Tool Change	T01 M06 – change to Tool 1
M08 / M09	Coolant On / Off	M08 – coolant on, M09 – coolant off
M30	End of Program + Reset	M30

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🧪 Real G-Code Program Example

G21 G90 G94        ; mm units, absolute, feed per minute
G17 G40 G49        ; XY plane, cancel radius/tool comp
T01 M06            ; Tool 1 change
G00 X0 Y0 Z5       ; Rapid move to start
G43 H01 Z5         ; Apply tool length offset
M03 S1500          ; Spindle on CW at 1500 RPM
G01 Z-1 F200       ; Feed into material
G01 X50 Y0         ; Linear cut
G02 X50 Y50 I0 J25 ; CW arc
G01 X0 Y50         ; Linear cut
M09                ; Coolant off
G00 Z5             ; Retract
M05 M30            ; Spindle stop, program end

This sample produces a square with a rounded corner—ideal for testing arcs and feedrate control.

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📊 G & M Code Cheat Sheet (Printable)

Function	Code
Rapid Position	G00
Feed Move	G01
Arc CW/CCW	G02 / G03
Spindle On CW	M03
Tool Change	M06
End Program	M30

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🚀 Future of CNC Programming

• Support for 5-axis G-code commands (e.g. G68, G43.4) in low-cost controllers
• Integration with AI-generated toolpaths
• Automatic syntax correction in CAM post-processors

The trend in CNC programming is moving toward automation, AI-enhanced logic, and safer command verification, especially in high-precision and high-speed machining environments.

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✅ Conclusion

Knowing your G-codes and M-codes is fundamental to CNC mastery. Whether you are debugging, programming from scratch, or verifying post-processor output, this guide gives you the tools you need to succeed.

Bookmark this page and explore more live code examples at cnccode.com.