G CODES: COMPLETE LIST AND GUIDE

G codes: Full list (Milling & Turning)

* Click the G Code to read the full explanation

What is a G code?

G-code is the common name for the most widely used CNC programming language. It was developed in the 1950s at MIT. The language is very “primitive” by today’s standards. All the commands are represented by codes (G01, G02, etc..) and not by meaningful words. Variables are represented by numbers(#500, #151, etc..) and not by words; conditional logic is very limited. Amazingly this 70-year-old language is still the industry standard. Several tool manufacturers developed higher-end Wizard-like languages such as Mazak – Mazatrol or Okuma – AOT, but none of them gained very high popularity.

The target of the code is to control the movements of a computerized controlled machine. The code basically “tells” the machine in what path to move from one coordinate to the next (Called “Toolpath”), and at what speed (Called “Feedrate”).

G code syntax

Sample short program

N10 O1000;

N20 T05;

N30 G01 A10 X40 Z60 F1.0 S1000;

N40 M05;

What does each letter in the program mean?

Letter	Role
X,Y,Z,A,B,C	Coordinates for Movement
F	Spindle Speed – The speed at which the spindle should be rotating.
S	Spindle Speed – The speed the spindle should be rotating.
I,J,K	Arc center for G02/G03
O	Program Number
N	Line (Block) Number
M	Miscellaneous function – See separate List
T	Select a tool from Magazine / Turret
P	Parameter Number

M Codes

“G” stands for Geometry; hence, the G-Code commands are responsible for the movements of the machine that create the geometry of the part. “M” stands for Machine (or Miscellaneous), and the M-Codes are responsible for Machine commands that cause particular operations of the equipment. Unlike G-codes, which can appear multiple times on the same line, M-Code is limited to one code per line.

List of M-codes

Code	Description	The spindle will start to rotate in CW direction at the speed given in the S parameter.
M00	Machine Stop	The Machine will stop the operation in the middle of the program
M01	Optional stop	The machine will stop in the middle of the program only if the optional stop button is “On”.
M02	program End	End of Program
M03	Spindle on CW direction	The spindle will start to rotate in CW direction at the speed given in the S parameter.
M04	Spindle on CCW direction	The spindle will start to rotate in CW direction at the speed given in the S parameter.
M05	Spindle stop	The spindle will stop rotating
M06	Automatic tool change (ATC)	The spindle will start to rotate in CCW direction at the speed given in the S parameter.
M07	Mist (Shower) Coolant On	A spray of coolant fluid droplets
M08	Flood Coolant On	An overflowing of coolant fluid.
M09	Coolant off	Shut down the coolant (Both M07 & M08)
M30	End of Program	The spindle will start to rotate in CW direction at the speed given in the S parameter
M41 – M44	Gear selection	Select the gear suitable for the spindle speed (ON lathe Machines)
M48	Feedrate override On	Placed at the end of the subprogram and returns the control to the main program one line after the line it was called from.
M49	Feedrate override Off	Operator feedratee override is ignored.
M98	Subprogram call	Passes control to the subprogram number provided in parameter P
M99	Subprogram end	The machine will change the tool and pick from the Turret/Magazine a new tool according to the “T” parameter.