diff --git a/docs/G-Codes.md b/docs/G-Codes.md
index 893993e85..e1ab0b955 100644
--- a/docs/G-Codes.md
+++ b/docs/G-Codes.md
@@ -459,6 +459,13 @@ parameters of an extruder stepper (as defined in an
 If EXTRUDER is not specified, it defaults to the stepper defined in
 the active hotend.
 
+#### SET_NOZZLE_DIAMETER
+`SET_NOZZLE_DIAMETER [EXTRUDER=<config_name>] DIAMETER=<diameter>`:
+Set a new value for the nozzle diameter of the specified extruder
+(as defined in an [extruder](Config_Reference.md#extruder) config section).
+If EXTRUDER is not specified, it defaults to the active hotend.
+Changed settings are not retained on Klipper reset.
+
 #### SET_EXTRUDER_ROTATION_DISTANCE
 `SET_EXTRUDER_ROTATION_DISTANCE EXTRUDER=<config_name>
 [DISTANCE=<distance>]`: Set a new value for the provided extruder
diff --git a/klippy/kinematics/extruder.py b/klippy/kinematics/extruder.py
index 684f4be71..34aa84b41 100644
--- a/klippy/kinematics/extruder.py
+++ b/klippy/kinematics/extruder.py
@@ -186,9 +186,15 @@ class PrinterExtruder:
             toolhead.set_extruder(self, 0.)
             gcode.register_command("M104", self.cmd_M104)
             gcode.register_command("M109", self.cmd_M109)
+            gcode.register_mux_command("SET_NOZZLE_DIAMETER", "EXTRUDER", None,
+                                       self.cmd_default_SET_NOZZLE_DIAMETER,
+                                       desc=self.cmd_SET_NOZZLE_DIAMETER_help)
         gcode.register_mux_command("ACTIVATE_EXTRUDER", "EXTRUDER",
                                    self.name, self.cmd_ACTIVATE_EXTRUDER,
                                    desc=self.cmd_ACTIVATE_EXTRUDER_help)
+        gcode.register_mux_command("SET_NOZZLE_DIAMETER", "EXTRUDER",
+                                   self.name, self.cmd_SET_NOZZLE_DIAMETER,
+                                   desc=self.cmd_SET_NOZZLE_DIAMETER_help)
     def get_status(self, eventtime):
         sts = self.heater.get_status(eventtime)
         sts['can_extrude'] = self.heater.can_extrude
@@ -287,6 +293,25 @@ class PrinterExtruder:
         toolhead.flush_step_generation()
         toolhead.set_extruder(self, self.last_position)
         self.printer.send_event("extruder:activate_extruder")
+    cmd_SET_NOZZLE_DIAMETER_help = "Set nozzle diameter"
+    def cmd_default_SET_NOZZLE_DIAMETER(self, gcmd):
+        extruder = self.printer.lookup_object('toolhead').get_extruder()
+        extruder.cmd_SET_NOZZLE_DIAMETER(gcmd)
+    def cmd_SET_NOZZLE_DIAMETER(self, gcmd):
+        diameter = gcmd.get_float('DIAMETER', above=.0)
+
+        toolhead = self.printer.lookup_object('toolhead')
+        toolhead.flush_step_generation()
+
+        self.nozzle_diameter = diameter
+        def_max_cross_section = 4. * self.nozzle_diameter**2
+        self.max_extrude_ratio = def_max_cross_section / self.filament_area
+
+        logging.info("Nozzle diameter changed to %.2f, max_extrude_ratio=%.6f",
+                    self.nozzle_diameter, self.max_extrude_ratio)
+        gcmd.respond_info("Nozzle diameter set to %.2fmm\n"
+                         "Max extrude ratio: %.6f"
+                         % (diameter, self.max_extrude_ratio))
 
 # Dummy extruder class used when a printer has no extruder at all
 class DummyExtruder: