G20 and G21 : Inches and Metric

Overview

• These G-Codes specify the dimension unit for the input data between "inches" (G20) and “mm” (G21) used for positioning commands.

Command Format

• Syntax: G20 or G21
  • G20 - Inch Mode
    • Feed (G1, G2, G3) and Rapid (G0) moves are interpreted in inches
    • Feed Rates are inches per minute
  • G21 - Metric Mode
    • Feed (G1, G2, G3) and Rapid (G0) moves are interpreted in millimeters after this command
    • Feed Rates are mm per minute

Examples

G21 // set program to millimeters             
G01 X25.4 F1000

• The G-code above will move X to 25.4 mm at 1000 mm/min

Details

• The default value at startup is G21
• Best Practices
  • Put this command on its own line.
  • Specify it at the start of the program, or whenever you’re unsure which units are currently active.