G20 means “all moves starting now have their units specified in inches ( imperial units )”.

G20's evil twin is G21, which means “all moves starting now have their units specified in millimeters ( metric units )”, which is the default when Smoothie starts.

An inch is 25.4 millimeters.

The command is used as such :

G20

Which means : units are now imperial until another G-code changes it ( modal command )

No parameters.

These resources are used as references for Gcode :

• LinuxCNC Gcode list
• Reprap Gcode list