image http://upload.wikimedia.org/wikipedia/commons/thumb/e/eb/English_length_units_graph.svg/605px-English_length_units_graph.svg.png style="width:300px"

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.

Format

The command is used as such :

G20

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

Parameters

No parameters.

Further reading

These resources are used as references for Gcode :