diff --git a/config/example-polar.cfg b/config/example-polar.cfg
index 76d5ad5b..4f79927f 100644
--- a/config/example-polar.cfg
+++ b/config/example-polar.cfg
@@ -10,7 +10,8 @@
 step_pin: ar54
 dir_pin: ar55
 enable_pin: !ar38
-step_distance: 0.001963495
+microsteps: 16
+gear_ratio: 80:16
 
 [stepper_arm]
 step_pin: ar60
diff --git a/config/example-rotary-delta.cfg b/config/example-rotary-delta.cfg
index 583b97ec..38ef9365 100644
--- a/config/example-rotary-delta.cfg
+++ b/config/example-rotary-delta.cfg
@@ -10,7 +10,8 @@
 step_pin: ar54
 dir_pin: ar55
 enable_pin: !ar38
-step_distance: 0.001963495
+microsteps: 16
+gear_ratio: 107.000:16, 60:16
 endstop_pin: ^ar2
 homing_speed: 50
 position_endstop: 252
@@ -21,14 +22,16 @@ lower_arm_length: 320.000
 step_pin: ar60
 dir_pin: ar61
 enable_pin: !ar56
-step_distance: 0.001963495
+microsteps: 16
+gear_ratio: 107.000:16, 60:16
 endstop_pin: ^ar15
 
 [stepper_c]
 step_pin: ar46
 dir_pin: ar48
 enable_pin: !ar62
-step_distance: 0.001963495
+microsteps: 16
+gear_ratio: 107.000:16, 60:16
 endstop_pin: ^ar19
 
 [extruder]
diff --git a/docs/Config_Changes.md b/docs/Config_Changes.md
index 0defb55a..6d4c03da 100644
--- a/docs/Config_Changes.md
+++ b/docs/Config_Changes.md
@@ -6,6 +6,12 @@ All dates in this document are approximate.
 
 # Changes
 
+20201218: Rotary delta and polar printers must now specify a
+`gear_ratio` for their rotary steppers, and they may no longer specify
+a `step_distance` parameter.  See the
+[config reference](Config_Reference.md#stepper) for the format of the
+new gear_ratio paramter.
+
 20201213: It is not valid to specify a Z "position_endstop" when using
 "probe:z_virtual_endstop".  An error will now be raised if a Z
 "position_endstop" is specified with "probe:z_virtual_endstop".
diff --git a/docs/Config_Reference.md b/docs/Config_Reference.md
index ac4424ec..92a147fb 100644
--- a/docs/Config_Reference.md
+++ b/docs/Config_Reference.md
@@ -127,9 +127,24 @@ enable_pin:
 #   Enable pin (default is enable high; use ! to indicate enable
 #   low). If this parameter is not provided then the stepper motor
 #   driver must always be enabled.
-step_distance:
-#   Distance in mm that each step causes the axis to travel. This
+rotation_distance:
+#   Distance (in mm) that the axis travels with one full rotation of
+#   the stepper motor. This parameter must be provided.
+microsteps:
+#   The number of microsteps the stepper motor driver uses. This
 #   parameter must be provided.
+#full_steps_per_rotation: 200
+#   The number of full steps for one rotation of the stepper motor.
+#   Set this to 200 for a 1.8 degree stepper motor or set to 400 for a
+#   0.9 degree motor. The default is 200.
+#gear_ratio:
+#   The gear ratio if the stepper motor is connected to the axis via a
+#   gearbox. For example, one may specify "5:1" if a 5 to 1 gearbox is
+#   in use. If the axis has multiple gearboxes one may specify a comma
+#   separated list of gear ratios (for example, "57:11, 2:1"). If a
+#   gear_ratio is specified then rotation_distance specifies the
+#   distance the axis travels for one full rotation of the final gear.
+#   The default is to not use a gear ratio.
 endstop_pin:
 #   Endstop switch detection pin. This parameter must be provided for
 #   the X, Y, and Z steppers on cartesian style printers.
@@ -367,11 +382,11 @@ kinematics: polar
 # The stepper_bed section is used to describe the stepper controlling
 # the bed.
 [stepper_bed]
-step_distance:
-#   On a polar printer the step_distance is the amount each step pulse
-#   moves the bed in radians (for example, a 1.8 degree stepper with
-#   16 micro-steps would be 2 * pi * (1.8 / 360) / 16 == 0.001963495).
-#   This parameter must be provided.
+gear_ratio:
+#   A gear_ratio must be specified and rotation_distance may not be
+#   specified. For example, if the bed has an 80 toothed pulley driven
+#   by a stepper with a 16 toothed pulley then one would specify a
+#   gear ratio of "80:16". This parameter must be provided.
 max_z_velocity:
 #   This sets the maximum velocity (in mm/s) of movement along the z
 #   axis. This setting can be used to restrict the maximum speed of
@@ -429,11 +444,13 @@ shoulder_height:
 # right arm (at 30 degrees). This section also controls the homing
 # parameters (homing_speed, homing_retract_dist) for all arms.
 [stepper_a]
-step_distance:
-#   On a rotary delta printer the step_distance is the amount each
-#   step pulse moves the upper arm in radians (for example, a directly
-#   connected 1.8 degree stepper with 16 micro-steps would be 2 * pi *
-#   (1.8 / 360) / 16 == 0.001963495). This parameter must be provided.
+gear_ratio:
+#   A gear_ratio must be specified and rotation_distance may not be
+#   specified. For example, if the arm has an 80 toothed pulley driven
+#   by a pulley with 16 teeth, which is in turn connected to a 60
+#   toothed pulley driven by a stepper with a 16 toothed pulley, then
+#   one would specify a gear ratio of "80:16, 60:16". This parameter
+#   must be provided.
 position_endstop:
 #   Distance (in mm) between the nozzle and the bed when the nozzle is
 #   in the center of the build area and the endstop triggers. This
@@ -501,10 +518,10 @@ kinematics: winch
 # cable winch. A minimum of 3 and a maximum of 26 cable winches may be
 # defined (stepper_a to stepper_z) though it is common to define 4.
 [stepper_a]
-step_distance:
-#   The step_distance is the nominal distance (in mm) the toolhead
-#   moves towards the cable winch on each step pulse. This parameter
-#   must be provided.
+rotation_distance:
+#   The rotation_distance is the nominal distance (in mm) the toolhead
+#   moves towards the cable winch for each full rotation of the
+#   stepper motor. This parameter must be provided.
 anchor_x:
 anchor_y:
 anchor_z:
@@ -541,7 +558,8 @@ tuning pressure advance.
 step_pin:
 dir_pin:
 enable_pin:
-step_distance:
+microsteps:
+rotation_distance:
 #   See the "stepper" section for a description of the above parameters.
 nozzle_diameter:
 #   Diameter of the nozzle orifice (in mm). This parameter must be
@@ -1613,7 +1631,8 @@ at 1 (for example, "stepper_z1", "stepper_z2", etc.).
 #step_pin:
 #dir_pin:
 #enable_pin:
-#step_distance:
+#microsteps:
+#rotation_distance:
 #   See the "stepper" section for the definition of the above parameters.
 #endstop_pin:
 #   If an endstop_pin is defined for the additional stepper then the
@@ -1670,7 +1689,8 @@ axis:
 #step_pin:
 #dir_pin:
 #enable_pin:
-#step_distance:
+#microsteps:
+#rotation_distance:
 #endstop_pin:
 #position_endstop:
 #position_min:
@@ -1695,7 +1715,8 @@ more information.
 #step_pin:
 #dir_pin:
 #enable_pin:
-#step_distance:
+#microsteps:
+#rotation_distance:
 #   See the "stepper" section for the definition of the above
 #   parameters.
 ```
@@ -1715,7 +1736,8 @@ normal printer kinematics.
 #step_pin:
 #dir_pin:
 #enable_pin:
-#step_distance:
+#microsteps:
+#rotation_distance:
 #   See the "stepper" section for a description of these parameters.
 #velocity:
 #   Set the default velocity (in mm/s) for the stepper. This value
@@ -2531,10 +2553,6 @@ cs_pin:
 #spi_software_miso_pin:
 #   See the "common SPI settings" section for a description of the
 #   above parameters.
-microsteps:
-#   The number of microsteps to configure the driver to use. Valid
-#   values are 1, 2, 4, 8, 16, 32, 64, 128, 256. This parameter must
-#   be provided.
 #interpolate: True
 #   If true, enable step interpolation (the driver will internally
 #   step at a rate of 256 micro-steps). The default is True.
@@ -2601,10 +2619,6 @@ uart_pin:
 #   A comma separated list of pins to set prior to accessing the
 #   tmc2208 UART. This may be useful for configuring an analog mux for
 #   UART communication. The default is to not configure any pins.
-microsteps:
-#   The number of microsteps to configure the driver to use. Valid
-#   values are 1, 2, 4, 8, 16, 32, 64, 128, 256. This parameter must
-#   be provided.
 #interpolate: True
 #   If true, enable step interpolation (the driver will internally
 #   step at a rate of 256 micro-steps). The default is True.
@@ -2654,7 +2668,6 @@ by the name of the corresponding stepper config section (for example,
 uart_pin:
 #tx_pin:
 #select_pins:
-#microsteps:
 #interpolate: True
 run_current:
 #hold_current:
@@ -2715,10 +2728,6 @@ cs_pin:
 #spi_software_miso_pin:
 #   See the "common SPI settings" section for a description of the
 #   above parameters.
-microsteps:
-#   The number of microsteps to configure the driver to use. Valid
-#   values are 1, 2, 4, 8, 16, 32, 64, 128, 256. This parameter must
-#   be provided.
 #interpolate: True
 #   If true, enable step interpolation (the driver will internally
 #   step at a rate of 256 micro-steps). This only works if microsteps
@@ -2786,10 +2795,6 @@ cs_pin:
 #spi_software_miso_pin:
 #   See the "common SPI settings" section for a description of the
 #   above parameters.
-microsteps:
-#   The number of microsteps to configure the driver to use. Valid
-#   values are 1, 2, 4, 8, 16, 32, 64, 128, 256. This parameter must
-#   be provided.
 #interpolate: True
 #   If true, enable step interpolation (the driver will internally
 #   step at a rate of 256 micro-steps). The default is True.
diff --git a/docs/Config_checks.md b/docs/Config_checks.md
index 7a5712a1..8065dd3d 100644
--- a/docs/Config_checks.md
+++ b/docs/Config_checks.md
@@ -100,7 +100,7 @@ then it generally indicates that the "dir_pin" for the axis needs to
 be inverted. This is done by adding a '!' to the "dir_pin" in the
 printer config file (or removing it if one is already there). If the
 motor moves significantly more or significantly less than one
-millimeter then verify the "step_distance" setting.
+millimeter then verify the "rotation_distance" setting.
 
 Run the above test for each stepper motor defined in the config
 file. (Set the STEPPER parameter of the STEPPER_BUZZ command to the
diff --git a/docs/FAQ.md b/docs/FAQ.md
index d571c1a9..7ea22430 100644
--- a/docs/FAQ.md
+++ b/docs/FAQ.md
@@ -262,9 +262,9 @@ around 10000 steps per second. If it is requested to move at a speed
 that would require a higher step rate then Marlin will generally just
 step as fast as it can. Klipper is able to achieve much higher step
 rates, but the stepper motor may not have sufficient torque to move at
-a higher speed. So, for a Z axis with a very precise step_distance the
-actual obtainable max_z_velocity may be smaller than what is
-configured in Marlin.
+a higher speed. So, for a Z axis with a high gearing ratio or high
+microsteps setting the actual obtainable max_z_velocity may be smaller
+than what is configured in Marlin.
 
 ### My TMC motor driver turns off in the middle of a print
 
diff --git a/docs/G-Codes.md b/docs/G-Codes.md
index dc9b5060..72cc3fea 100644
--- a/docs/G-Codes.md
+++ b/docs/G-Codes.md
@@ -172,8 +172,10 @@ The following standard commands are supported:
   [SMOOTH_TIME=<pressure_advance_smooth_time>]`: Set pressure advance
   parameters. If EXTRUDER is not specified, it defaults to the active
   extruder.
-- `SET_EXTRUDER_STEP_DISTANCE [EXTRUDER=<config_name>] [DISTANCE=<distance>]`:
-  Set a new value for the provided extruder's step_distance. Value is
+- `SET_EXTRUDER_STEP_DISTANCE [EXTRUDER=<config_name>]
+  [DISTANCE=<distance>]`: Set a new value for the provided extruder's
+  "step distance". The "step distance" is
+  `rotation_distance/(full_steps_per_rotation*microsteps)`. Value is
   not retained on Klipper reset. Use with caution, small changes can
   result in excessive pressure between extruder and hot end. Do proper
   calibration steps with filament before use. If 'DISTANCE' value is
diff --git a/docs/Probe_Calibrate.md b/docs/Probe_Calibrate.md
index 9b7a08e5..48216174 100644
--- a/docs/Probe_Calibrate.md
+++ b/docs/Probe_Calibrate.md
@@ -114,11 +114,12 @@ Recv: // probe accuracy results: maximum 2.519448, minimum 2.506948, range 0.012
 Ideally the tool will report an identical maximum and minimum value.
 (That is, ideally the probe obtains an identical result on all ten
 probes.) However, it's normal for the minimum and maximum values to
-differ by one Z step_distance or up to 5 microns (.005mm). The
-distance between the minimum and the maximum value is called the
-range. So, in the above example, since the printer uses a Z
-step_distance of .0125, a range of 0.012500 would be considered
-normal.
+differ by one Z "step distance" or up to 5 microns (.005mm). A "step
+distance" is
+`rotation_distance/(full_steps_per_rotation*microsteps)`. The distance
+between the minimum and the maximum value is called the range. So, in
+the above example, since the printer uses a Z step distance of .0125,
+a range of 0.012500 would be considered normal.
 
 If the results of the test show a range value that is greater than 25
 microns (.025mm) then the probe does not have sufficient accuracy for
diff --git a/klippy/extras/tmc.py b/klippy/extras/tmc.py
index 7b9280dd..c14a5f0f 100644
--- a/klippy/extras/tmc.py
+++ b/klippy/extras/tmc.py
@@ -1,9 +1,10 @@
 # Common helper code for TMC stepper drivers
 #
-# Copyright (C) 2018-2019  Kevin O'Connor <kevin@koconnor.net>
+# Copyright (C) 2018-2020  Kevin O'Connor <kevin@koconnor.net>
 #
 # This file may be distributed under the terms of the GNU GPLv3 license.
 import logging, collections
+import stepper
 
 
 ######################################################################
@@ -263,9 +264,14 @@ class TMCMicrostepHelper:
     def __init__(self, config, mcu_tmc):
         self.mcu_tmc = mcu_tmc
         self.fields = mcu_tmc.get_fields()
+        stepper_name = " ".join(config.get_name().split()[1:])
+        stepper_config = ms_config = config.getsection(stepper_name)
+        if stepper_config.get('microsteps', None, note_valid=False) is None:
+            # Older config format with microsteps in tmc config section
+            ms_config = config
         steps = {'256': 0, '128': 1, '64': 2, '32': 3, '16': 4,
                  '8': 5, '4': 6, '2': 7, '1': 8}
-        mres = config.getchoice('microsteps', steps)
+        mres = ms_config.getchoice('microsteps', steps)
         self.fields.set_field("MRES", mres)
         self.fields.set_field("intpol", config.getboolean("interpolate", True))
     def get_microsteps(self):
@@ -287,7 +293,7 @@ def TMCStealthchopHelper(config, mcu_tmc, tmc_freq):
     if velocity:
         stepper_name = " ".join(config.get_name().split()[1:])
         stepper_config = config.getsection(stepper_name)
-        step_dist = stepper_config.getfloat('step_distance', note_valid=False)
+        step_dist = stepper.parse_step_distance(stepper_config)
         step_dist_256 = step_dist / (1 << fields.get_field("MRES"))
         threshold = int(tmc_freq * step_dist_256 / velocity + .5)
         fields.set_field("TPWMTHRS", max(0, min(0xfffff, threshold)))
diff --git a/klippy/stepper.py b/klippy/stepper.py
index a8ab2298..1b1ad7ad 100644
--- a/klippy/stepper.py
+++ b/klippy/stepper.py
@@ -183,7 +183,7 @@ def PrinterStepper(config, units_in_radians=False):
     step_pin_params = ppins.lookup_pin(step_pin, can_invert=True)
     dir_pin = config.get('dir_pin')
     dir_pin_params = ppins.lookup_pin(dir_pin, can_invert=True)
-    step_dist = config.getfloat('step_distance', above=0.)
+    step_dist = parse_step_distance(config, units_in_radians, True)
     mcu_stepper = MCU_stepper(name, step_pin_params, dir_pin_params, step_dist,
                               units_in_radians)
     # Support for stepper enable pin handling
@@ -194,6 +194,47 @@ def PrinterStepper(config, units_in_radians=False):
     force_move.register_stepper(mcu_stepper)
     return mcu_stepper
 
+# Parse stepper gear_ratio config parameter
+def parse_gear_ratio(config, note_valid):
+    gear_ratio = config.get('gear_ratio', None, note_valid=note_valid)
+    if gear_ratio is None:
+        return 1.
+    result = 1.
+    try:
+        gears = gear_ratio.split(',')
+        for gear in gears:
+            g1, g2 = [float(v.strip()) for v in gear.split(':')]
+            result *= g1 / g2
+    except:
+        raise config.error("Unable to parse gear_ratio: %s" % (gear_ratio,))
+    return result
+
+# Obtain "step distance" information from a config section
+def parse_step_distance(config, units_in_radians=None, note_valid=False):
+    if units_in_radians is None:
+        # Caller doesn't know if units are in radians - infer it
+        rd = config.get('rotation_distance', None, note_valid=False)
+        gr = config.get('gear_ratio', None, note_valid=False)
+        units_in_radians = rd is None and gr is not None
+    if units_in_radians:
+        rotation_dist = 2. * math.pi
+        config.get('gear_ratio', note_valid=note_valid)
+    else:
+        rotation_dist = config.getfloat('rotation_distance', None,
+                                        above=0., note_valid=note_valid)
+    if rotation_dist is None:
+        # Older config format with step_distance
+        return config.getfloat('step_distance', above=0., note_valid=note_valid)
+    # Newer config format with rotation_distance
+    microsteps = config.getint('microsteps', minval=1, note_valid=note_valid)
+    full_steps = config.getint('full_steps_per_rotation', 200, minval=1,
+                               note_valid=note_valid)
+    if full_steps % 4:
+        raise config.error("full_steps_per_rotation invalid in section '%s'"
+                           % (config.get_name(),))
+    gearing = parse_gear_ratio(config, note_valid)
+    return rotation_dist / (full_steps * microsteps * gearing)
+
 
 ######################################################################
 # Stepper controlled rails
diff --git a/test/klippy/rotary_delta_calibrate.cfg b/test/klippy/rotary_delta_calibrate.cfg
index ff42ff09..6709ce90 100644
--- a/test/klippy/rotary_delta_calibrate.cfg
+++ b/test/klippy/rotary_delta_calibrate.cfg
@@ -3,7 +3,8 @@
 step_pin: ar54
 dir_pin: ar55
 enable_pin: !ar38
-step_distance: 0.000010
+microsteps: 16
+gear_ratio: 107.000:16, 60:16
 endstop_pin: ^ar2
 homing_speed: 50
 #position_endstop: 252
@@ -14,14 +15,16 @@ lower_arm_length: 320.000
 step_pin: ar60
 dir_pin: ar61
 enable_pin: !ar56
-step_distance: 0.000010
+microsteps: 16
+gear_ratio: 107.000:16, 60:16
 endstop_pin: ^ar15
 
 [stepper_c]
 step_pin: ar46
 dir_pin: ar48
 enable_pin: !ar62
-step_distance: 0.000010
+microsteps: 16
+gear_ratio: 107.000:16, 60:16
 endstop_pin: ^ar19
 
 [mcu]