diff --git a/config/example.cfg b/config/example.cfg
index a086977c..f0e77e50 100644
--- a/config/example.cfg
+++ b/config/example.cfg
@@ -120,7 +120,7 @@ filament_diameter: 3.500
 #   extruder motor for retractions and extrude-only moves. These
 #   settings do not place any limit on normal printing moves. If not
 #   specified then they are calculated to match the limit an XY
-#   printing move with a max_extrude_cross_section extrusion would
+#   printing move with a cross section of 4.0*nozzle_diameter^2 would
 #   have.
 #pressure_advance: 0.0
 #   The amount of raw filament to push into the extruder during
diff --git a/klippy/kinematics/extruder.py b/klippy/kinematics/extruder.py
index c672bda2..f3821d05 100644
--- a/klippy/kinematics/extruder.py
+++ b/klippy/kinematics/extruder.py
@@ -23,18 +23,19 @@ class PrinterExtruder:
         filament_diameter = config.getfloat(
             'filament_diameter', minval=self.nozzle_diameter)
         self.filament_area = math.pi * (filament_diameter * .5)**2
+        def_max_cross_section = 4. * self.nozzle_diameter**2
+        def_max_extrude_ratio = def_max_cross_section / self.filament_area
         max_cross_section = config.getfloat(
-            'max_extrude_cross_section', 4. * self.nozzle_diameter**2
-            , above=0.)
+            'max_extrude_cross_section', def_max_cross_section, above=0.)
         self.max_extrude_ratio = max_cross_section / self.filament_area
         logging.info("Extruder max_extrude_ratio=%.6f", self.max_extrude_ratio)
         toolhead = self.printer.lookup_object('toolhead')
         max_velocity, max_accel = toolhead.get_max_velocity()
         self.max_e_velocity = config.getfloat(
-            'max_extrude_only_velocity', max_velocity * self.max_extrude_ratio
+            'max_extrude_only_velocity', max_velocity * def_max_extrude_ratio
             , above=0.)
         self.max_e_accel = config.getfloat(
-            'max_extrude_only_accel', max_accel * self.max_extrude_ratio
+            'max_extrude_only_accel', max_accel * def_max_extrude_ratio
             , above=0.)
         self.stepper.set_max_jerk(9999999.9, 9999999.9)
         self.max_e_dist = config.getfloat(