diff --git a/Marlin/Marlin_main.cpp b/Marlin/Marlin_main.cpp
index b19c86a77..ff35b97ec 100644
--- a/Marlin/Marlin_main.cpp
+++ b/Marlin/Marlin_main.cpp
@@ -5312,7 +5312,7 @@ void home_all_axes() { gcode_G28(true); }
   constexpr uint8_t _7P_STEP = 1,              // 7-point step - to change number of calibration points
                     _4P_STEP = _7P_STEP * 2,   // 4-point step
                     NPP      = _7P_STEP * 6;   // number of calibration points on the radius
-  enum CalEnum {                               // the 7 main calibration points - add definitions if needed
+  enum CalEnum : char {                               // the 7 main calibration points - add definitions if needed
     CEN      = 0,
     __A      = 1,
     _AB      = __A + _7P_STEP,
diff --git a/Marlin/enum.h b/Marlin/enum.h
index 13858971e..b4e7564f5 100644
--- a/Marlin/enum.h
+++ b/Marlin/enum.h
@@ -33,8 +33,7 @@
  *  - X_HEAD and Y_HEAD is used for systems that don't have a 1:1 relationship
  *    between X_AXIS and X Head movement, like CoreXY bots
  */
-enum AxisEnum {
-  NO_AXIS   = -1,
+enum AxisEnum : unsigned char {
   X_AXIS    = 0,
   A_AXIS    = 0,
   Y_AXIS    = 1,
@@ -45,7 +44,8 @@ enum AxisEnum {
   X_HEAD    = 4,
   Y_HEAD    = 5,
   Z_HEAD    = 6,
-  ALL_AXES  = 100
+  ALL_AXES  = 0xFE,
+  NO_AXIS   = 0xFF
 };
 
 #define LOOP_S_LE_N(VAR, S, N) for (uint8_t VAR=S; VAR<=N; VAR++)
@@ -76,7 +76,7 @@ typedef enum {
  * Debug flags
  * Not yet widely applied
  */
-enum DebugFlags {
+enum DebugFlags : unsigned char {
   DEBUG_NONE          = 0,
   DEBUG_ECHO          = _BV(0), ///< Echo commands in order as they are processed
   DEBUG_INFO          = _BV(1), ///< Print messages for code that has debug output
@@ -88,7 +88,7 @@ enum DebugFlags {
   DEBUG_ALL           = 0xFF
 };
 
-enum EndstopEnum {
+enum EndstopEnum : char {
   X_MIN,
   Y_MIN,
   Z_MIN,
@@ -105,7 +105,7 @@ enum EndstopEnum {
 };
 
 #if ENABLED(EMERGENCY_PARSER)
-  enum e_parser_state {
+  enum e_parser_state : char {
     state_RESET,
     state_N,
     state_M,
@@ -122,14 +122,14 @@ enum EndstopEnum {
 #endif
 
 #if ENABLED(ADVANCED_PAUSE_FEATURE)
-  enum AdvancedPauseMenuResponse {
+  enum AdvancedPauseMenuResponse : char {
     ADVANCED_PAUSE_RESPONSE_WAIT_FOR,
     ADVANCED_PAUSE_RESPONSE_EXTRUDE_MORE,
     ADVANCED_PAUSE_RESPONSE_RESUME_PRINT
   };
 
   #if ENABLED(ULTIPANEL)
-    enum AdvancedPauseMessage {
+    enum AdvancedPauseMessage : char {
       ADVANCED_PAUSE_MESSAGE_INIT,
       ADVANCED_PAUSE_MESSAGE_UNLOAD,
       ADVANCED_PAUSE_MESSAGE_INSERT,
@@ -143,7 +143,7 @@ enum EndstopEnum {
     };
   #endif
 
-  enum AdvancedPauseMode {
+  enum AdvancedPauseMode : char {
     ADVANCED_PAUSE_MODE_PAUSE_PRINT,
     ADVANCED_PAUSE_MODE_LOAD_FILAMENT,
     ADVANCED_PAUSE_MODE_UNLOAD_FILAMENT
@@ -155,7 +155,7 @@ enum EndstopEnum {
  * Marlin sends messages if blocked or busy
  */
 #if ENABLED(HOST_KEEPALIVE_FEATURE)
-  enum MarlinBusyState {
+  enum MarlinBusyState : char {
     NOT_BUSY,           // Not in a handler
     IN_HANDLER,         // Processing a GCode
     IN_PROCESS,         // Known to be blocking command input (as in G29)
@@ -167,12 +167,12 @@ enum EndstopEnum {
 /**
  * SD Card
  */
-enum LsAction { LS_SerialPrint, LS_Count, LS_GetFilename };
+enum LsAction : char { LS_SerialPrint, LS_Count, LS_GetFilename };
 
 /**
  * Ultra LCD
  */
-enum LCDViewAction {
+enum LCDViewAction : char {
   LCDVIEW_NONE,
   LCDVIEW_REDRAW_NOW,
   LCDVIEW_CALL_REDRAW_NEXT,
@@ -184,7 +184,7 @@ enum LCDViewAction {
  * Dual X Carriage modes. A Dual Nozzle can also do duplication.
  */
 #if ENABLED(DUAL_X_CARRIAGE) || ENABLED(DUAL_NOZZLE_DUPLICATION_MODE)
-  enum DualXMode {
+  enum DualXMode : char {
     DXC_FULL_CONTROL_MODE,  // DUAL_X_CARRIAGE only
     DXC_AUTO_PARK_MODE,     // DUAL_X_CARRIAGE only
     DXC_DUPLICATION_MODE
@@ -196,7 +196,7 @@ enum LCDViewAction {
  * (and "canned cycles" - not a current feature)
  */
 #if ENABLED(CNC_WORKSPACE_PLANES)
-  enum WorkspacePlane { PLANE_XY, PLANE_ZX, PLANE_YZ };
+  enum WorkspacePlane : char { PLANE_XY, PLANE_ZX, PLANE_YZ };
 #endif
 
 #endif // __ENUM_H__
diff --git a/Marlin/fastio.h b/Marlin/fastio.h
index 0f7df9765..50a37ffb8 100644
--- a/Marlin/fastio.h
+++ b/Marlin/fastio.h
@@ -41,7 +41,6 @@ typedef int8_t pin_t;
 #define AVR_ATmega2561_FAMILY (defined(__AVR_ATmega1281__) || defined(__AVR_ATmega2561__))
 #define AVR_ATmega328_FAMILY (defined(__AVR_ATmega168__) || defined(__AVR_ATmega328__) || defined(__AVR_ATmega328p__))
 
-
 /**
  * Include Ports and Functions
  */
@@ -118,7 +117,7 @@ typedef int8_t pin_t;
  */
 
 // Waveform Generation Modes
-typedef enum {
+enum WaveGenMode : char {
   WGM_NORMAL,          //  0
   WGM_PWM_PC_8,        //  1
   WGM_PWM_PC_9,        //  2
@@ -135,18 +134,18 @@ typedef enum {
   WGM_reserved,        // 13
   WGM_FAST_PWM_ICRn,   // 14  COM OCnA
   WGM_FAST_PWM_OCRnA   // 15  COM OCnA
-} WaveGenMode;
+};
 
 // Compare Modes
-typedef enum {
+enum CompareMode : char {
   COM_NORMAL,          //  0
   COM_TOGGLE,          //  1  Non-PWM: OCnx ... Both PWM (WGM 9,11,14,15): OCnA only ... else NORMAL
   COM_CLEAR_SET,       //  2  Non-PWM: OCnx ... Fast PWM: OCnx/Bottom ... PF-FC: OCnx Up/Down
   COM_SET_CLEAR        //  3  Non-PWM: OCnx ... Fast PWM: OCnx/Bottom ... PF-FC: OCnx Up/Down
-} CompareMode;
+};
 
 // Clock Sources
-typedef enum {
+enum ClockSource : char {
   CS_NONE,             //  0
   CS_PRESCALER_1,      //  1
   CS_PRESCALER_8,      //  2
@@ -155,10 +154,10 @@ typedef enum {
   CS_PRESCALER_1024,   //  5
   CS_EXT_FALLING,      //  6
   CS_EXT_RISING        //  7
-} ClockSource;
+};
 
 // Clock Sources (Timer 2 only)
-typedef enum {
+enum ClockSource2 : char {
   CS2_NONE,            //  0
   CS2_PRESCALER_1,     //  1
   CS2_PRESCALER_8,     //  2
@@ -167,7 +166,7 @@ typedef enum {
   CS2_PRESCALER_128,   //  5
   CS2_PRESCALER_256,   //  6
   CS2_PRESCALER_1024   //  7
-} ClockSource2;
+};
 
 // Get interrupt bits in an orderly way
 #define GET_WGM(T)   (((TCCR##T##A >> WGM##T##0) & 0x3) | ((TCCR##T##B >> WGM##T##2 << 2) & 0xC))
diff --git a/Marlin/mesh_bed_leveling.h b/Marlin/mesh_bed_leveling.h
index 11e3150ab..f3a374af5 100644
--- a/Marlin/mesh_bed_leveling.h
+++ b/Marlin/mesh_bed_leveling.h
@@ -25,7 +25,7 @@
 
 #include "MarlinConfig.h"
 
-enum MeshLevelingState {
+enum MeshLevelingState : char {
   MeshReport,
   MeshStart,
   MeshNext,
diff --git a/Marlin/planner.h b/Marlin/planner.h
index d55fa0da0..bc0a39d5e 100644
--- a/Marlin/planner.h
+++ b/Marlin/planner.h
@@ -40,7 +40,7 @@
   #include "vector_3.h"
 #endif
 
-enum BlockFlagBit {
+enum BlockFlagBit : char {
   // Recalculate trapezoids on entry junction. For optimization.
   BLOCK_BIT_RECALCULATE,
 
@@ -56,7 +56,7 @@ enum BlockFlagBit {
   BLOCK_BIT_CONTINUED
 };
 
-enum BlockFlag {
+enum BlockFlag : char {
   BLOCK_FLAG_RECALCULATE          = _BV(BLOCK_BIT_RECALCULATE),
   BLOCK_FLAG_NOMINAL_LENGTH       = _BV(BLOCK_BIT_NOMINAL_LENGTH),
   BLOCK_FLAG_BUSY                 = _BV(BLOCK_BIT_BUSY),
diff --git a/Marlin/stopwatch.h b/Marlin/stopwatch.h
index 74eb72e8d..f5ac78bfa 100644
--- a/Marlin/stopwatch.h
+++ b/Marlin/stopwatch.h
@@ -36,7 +36,7 @@
  */
 class Stopwatch {
   private:
-    enum State {
+    enum State : char {
       STOPPED,
       RUNNING,
       PAUSED
diff --git a/Marlin/temperature.h b/Marlin/temperature.h
index c43776a5d..710c9c23f 100644
--- a/Marlin/temperature.h
+++ b/Marlin/temperature.h
@@ -56,7 +56,7 @@
 /**
  * States for ADC reading in the ISR
  */
-enum ADCSensorState {
+enum ADCSensorState : char {
   #if HAS_TEMP_0
     PrepareTemp_0,
     MeasureTemp_0,
@@ -613,7 +613,7 @@ class Temperature {
 
     #if ENABLED(THERMAL_PROTECTION_HOTENDS) || HAS_THERMALLY_PROTECTED_BED
 
-      typedef enum TRState { TRInactive, TRFirstHeating, TRStable, TRRunaway } TRstate;
+      enum TRState : char { TRInactive, TRFirstHeating, TRStable, TRRunaway };
 
       static void thermal_runaway_protection(TRState * const state, millis_t * const timer, const float &current, const float &target, const int8_t heater_id, const uint16_t period_seconds, const uint16_t hysteresis_degc);
 
diff --git a/Marlin/tmc_util.cpp b/Marlin/tmc_util.cpp
index 2778d9963..9b2c35582 100644
--- a/Marlin/tmc_util.cpp
+++ b/Marlin/tmc_util.cpp
@@ -251,7 +251,7 @@ void _tmc_say_sgt(const TMC_AxisEnum axis, const int8_t sgt) {
 
 #if ENABLED(TMC_DEBUG)
 
-  enum TMC_debug_enum {
+  enum TMC_debug_enum : char {
     TMC_CODES,
     TMC_ENABLED,
     TMC_CURRENT,
@@ -275,7 +275,7 @@ void _tmc_say_sgt(const TMC_AxisEnum axis, const int8_t sgt) {
     TMC_HSTRT,
     TMC_SGT
   };
-  enum TMC_drv_status_enum {
+  enum TMC_drv_status_enum : char {
     TMC_DRV_CODES,
     TMC_STST,
     TMC_OLB,
diff --git a/Marlin/tmc_util.h b/Marlin/tmc_util.h
index aa1fb6329..acd3ff8fe 100644
--- a/Marlin/tmc_util.h
+++ b/Marlin/tmc_util.h
@@ -29,7 +29,7 @@
 
 extern bool report_tmc_status;
 
-enum TMC_AxisEnum { TMC_X, TMC_X2, TMC_Y, TMC_Y2, TMC_Z, TMC_Z2, TMC_E0, TMC_E1, TMC_E2, TMC_E3, TMC_E4 };
+enum TMC_AxisEnum : char { TMC_X, TMC_X2, TMC_Y, TMC_Y2, TMC_Z, TMC_Z2, TMC_E0, TMC_E1, TMC_E2, TMC_E3, TMC_E4 };
 
 constexpr uint32_t _tmc_thrs(const uint16_t msteps, const int32_t thrs, const uint32_t spmm) {
   return 12650000UL * msteps / (256 * thrs * spmm);
diff --git a/Marlin/ubl.h b/Marlin/ubl.h
index 0a54c7c7a..4b0316974 100644
--- a/Marlin/ubl.h
+++ b/Marlin/ubl.h
@@ -50,7 +50,7 @@
 
 // ubl_G29.cpp
 
-enum MeshPointType { INVALID, REAL, SET_IN_BITMAP };
+enum MeshPointType : char { INVALID, REAL, SET_IN_BITMAP };
 
 // External references