diff --git a/tests/phpunit/tests/theme/wpThemeJson.php b/tests/phpunit/tests/theme/wpThemeJson.php
index 8fef9c29b861c..0b54d99cbaa72 100644
--- a/tests/phpunit/tests/theme/wpThemeJson.php
+++ b/tests/phpunit/tests/theme/wpThemeJson.php
@@ -3093,9 +3093,9 @@ public function test_get_property_value_self() {
 	 * @param array $layout_definitions Layout definitions as stored in core theme.json.
 	 */
 	public function test_get_stylesheet_generates_layout_styles( $layout_definitions ) {
-		$theme_json = new WP_Theme_JSON_Gutenberg(
+		$theme_json = new WP_Theme_JSON(
 			array(
-				'version'  => WP_Theme_JSON_Gutenberg::LATEST_SCHEMA,
+				'version'  => WP_Theme_JSON::LATEST_SCHEMA,
 				'settings' => array(
 					'layout'  => array(
 						'definitions' => $layout_definitions,
@@ -3128,9 +3128,9 @@ public function test_get_stylesheet_generates_layout_styles( $layout_definitions
 	 * @param array $layout_definitions Layout definitions as stored in core theme.json.
 	 */
 	public function test_get_stylesheet_generates_layout_styles_with_spacing_presets( $layout_definitions ) {
-		$theme_json = new WP_Theme_JSON_Gutenberg(
+		$theme_json = new WP_Theme_JSON(
 			array(
-				'version'  => WP_Theme_JSON_Gutenberg::LATEST_SCHEMA,
+				'version'  => WP_Theme_JSON::LATEST_SCHEMA,
 				'settings' => array(
 					'layout'  => array(
 						'definitions' => $layout_definitions,
@@ -3163,9 +3163,9 @@ public function test_get_stylesheet_generates_layout_styles_with_spacing_presets
 	 * @param array $layout_definitions Layout definitions as stored in core theme.json.
 	 */
 	public function test_get_stylesheet_generates_fallback_gap_layout_styles( $layout_definitions ) {
-		$theme_json = new WP_Theme_JSON_Gutenberg(
+		$theme_json = new WP_Theme_JSON(
 			array(
-				'version'  => WP_Theme_JSON_Gutenberg::LATEST_SCHEMA,
+				'version'  => WP_Theme_JSON::LATEST_SCHEMA,
 				'settings' => array(
 					'layout'  => array(
 						'definitions' => $layout_definitions,
@@ -3199,9 +3199,9 @@ public function test_get_stylesheet_generates_fallback_gap_layout_styles( $layou
 	 * @param array $layout_definitions Layout definitions as stored in core theme.json.
 	 */
 	public function test_get_stylesheet_generates_base_fallback_gap_layout_styles( $layout_definitions ) {
-		$theme_json = new WP_Theme_JSON_Gutenberg(
+		$theme_json = new WP_Theme_JSON(
 			array(
-				'version'  => WP_Theme_JSON_Gutenberg::LATEST_SCHEMA,
+				'version'  => WP_Theme_JSON::LATEST_SCHEMA,
 				'settings' => array(
 					'layout'  => array(
 						'definitions' => $layout_definitions,
@@ -3231,9 +3231,9 @@ public function test_get_stylesheet_generates_base_fallback_gap_layout_styles( $
 	 */
 	public function test_get_stylesheet_skips_layout_styles( $layout_definitions ) {
 		add_theme_support( 'disable-layout-styles' );
-		$theme_json = new WP_Theme_JSON_Gutenberg(
+		$theme_json = new WP_Theme_JSON(
 			array(
-				'version'  => WP_Theme_JSON_Gutenberg::LATEST_SCHEMA,
+				'version'  => WP_Theme_JSON::LATEST_SCHEMA,
 				'settings' => array(
 					'layout'  => array(
 						'definitions' => $layout_definitions,
@@ -3340,11 +3340,346 @@ public function data_get_layout_definitions() {
 		);
 	}
 
+	/**
+	 * Tests generating the spacing presets array based on the spacing scale provided.
+	 *
+	 * @ticket 56467
+	 *
+	 * @dataProvider data_generate_spacing_scale_fixtures
+	 */
+	function test_set_spacing_sizes( $spacing_scale, $expected_output ) {
+		$theme_json = new WP_Theme_JSON(
+			array(
+				'version'  => 2,
+				'settings' => array(
+					'spacing' => array(
+						'spacingScale' => $spacing_scale,
+					),
+				),
+			)
+		);
+
+		$theme_json->set_spacing_sizes();
+		$this->assertSame( $expected_output, _wp_array_get( $theme_json->get_raw_data(), array( 'settings', 'spacing', 'spacingSizes', 'default' ) ) );
+	}
+
+	/**
+	 * Data provider for spacing scale tests.
+	 *
+	 * @ticket 56467
+	 *
+	 * @return array
+	 */
+	function data_generate_spacing_scale_fixtures() {
+		return array(
+			'one_step_spacing_scale' => array(
+				'spacingScale'    => array(
+					'operator'   => '+',
+					'increment'  => 1.5,
+					'steps'      => 1,
+					'mediumStep' => 4,
+					'unit'       => 'rem',
+				),
+				'expected_output' => array(
+					array(
+						'name' => 'Medium',
+						'slug' => '50',
+						'size' => '4rem',
+					),
+				),
+			),
+
+			'two_step_spacing_scale_should_add_step_above_medium' => array(
+				'spacingScale'    => array(
+					'operator'   => '+',
+					'increment'  => 1.5,
+					'steps'      => 2,
+					'mediumStep' => 4,
+					'unit'       => 'rem',
+				),
+				'expected_output' => array(
+					array(
+						'name' => 'Medium',
+						'slug' => '50',
+						'size' => '4rem',
+					),
+					array(
+						'name' => 'Large',
+						'slug' => '60',
+						'size' => '5.5rem',
+					),
+				),
+			),
+
+			'three_step_spacing_scale_should_add_step_above_and_below_medium' => array(
+				'spacingScale'    => array(
+					'operator'   => '+',
+					'increment'  => 1.5,
+					'steps'      => 3,
+					'mediumStep' => 4,
+					'unit'       => 'rem',
+				),
+				'expected_output' => array(
+					array(
+						'name' => 'Small',
+						'slug' => '40',
+						'size' => '2.5rem',
+					),
+					array(
+						'name' => 'Medium',
+						'slug' => '50',
+						'size' => '4rem',
+					),
+					array(
+						'name' => 'Large',
+						'slug' => '60',
+						'size' => '5.5rem',
+					),
+				),
+			),
+
+			'even_step_spacing_scale_steps_should_add_extra_step_above_medium' => array(
+				'spacingScale'    => array(
+					'operator'   => '+',
+					'increment'  => 1.5,
+					'steps'      => 4,
+					'mediumStep' => 4,
+					'unit'       => 'rem',
+				),
+				'expected_output' => array(
+					array(
+						'name' => 'Small',
+						'slug' => '40',
+						'size' => '2.5rem',
+					),
+					array(
+						'name' => 'Medium',
+						'slug' => '50',
+						'size' => '4rem',
+					),
+					array(
+						'name' => 'Large',
+						'slug' => '60',
+						'size' => '5.5rem',
+					),
+					array(
+						'name' => 'X-Large',
+						'slug' => '70',
+						'size' => '7rem',
+					),
+				),
+			),
+
+			'if_bottom_end_will_go_below_zero_should_add_extra_steps_above_medium_instead' => array(
+				'spacingScale'    => array(
+					'operator'   => '+',
+					'increment'  => 2.5,
+					'steps'      => 5,
+					'mediumStep' => 5,
+					'unit'       => 'rem',
+				),
+				'expected_output' => array(
+					array(
+						'name' => 'Small',
+						'slug' => '40',
+						'size' => '2.5rem',
+					),
+					array(
+						'name' => 'Medium',
+						'slug' => '50',
+						'size' => '5rem',
+					),
+					array(
+						'name' => 'Large',
+						'slug' => '60',
+						'size' => '7.5rem',
+					),
+					array(
+						'name' => 'X-Large',
+						'slug' => '70',
+						'size' => '10rem',
+					),
+					array(
+						'name' => '2X-Large',
+						'slug' => '80',
+						'size' => '12.5rem',
+					),
+				),
+			),
+
+			'multiplier_should_correctly_calculate_above_and_below_medium' => array(
+				'spacingScale'    => array(
+					'operator'   => '*',
+					'increment'  => 1.5,
+					'steps'      => 5,
+					'mediumStep' => 1.5,
+					'unit'       => 'rem',
+				),
+				'expected_output' => array(
+					array(
+						'name' => 'X-Small',
+						'slug' => '30',
+						'size' => '0.67rem',
+					),
+					array(
+						'name' => 'Small',
+						'slug' => '40',
+						'size' => '1rem',
+					),
+					array(
+						'name' => 'Medium',
+						'slug' => '50',
+						'size' => '1.5rem',
+					),
+					array(
+						'name' => 'Large',
+						'slug' => '60',
+						'size' => '2.25rem',
+					),
+					array(
+						'name' => 'X-Large',
+						'slug' => '70',
+						'size' => '3.38rem',
+					),
+				),
+			),
+
+			'increment_<_1_combined_with_*_operator_should_act_as_divisor_to_calculate_above_and_below_medium' => array(
+				'spacingScale'    => array(
+					'operator'   => '*',
+					'increment'  => 0.25,
+					'steps'      => 5,
+					'mediumStep' => 1.5,
+					'unit'       => 'rem',
+				),
+				'expected_output' => array(
+					array(
+						'name' => 'X-Small',
+						'slug' => '30',
+						'size' => '0.09rem',
+					),
+					array(
+						'name' => 'Small',
+						'slug' => '40',
+						'size' => '0.38rem',
+					),
+					array(
+						'name' => 'Medium',
+						'slug' => '50',
+						'size' => '1.5rem',
+					),
+					array(
+						'name' => 'Large',
+						'slug' => '60',
+						'size' => '6rem',
+					),
+					array(
+						'name' => 'X-Large',
+						'slug' => '70',
+						'size' => '24rem',
+					),
+				),
+			),
+		);
+	}
+
+	/**
+	 * Tests generating the spacing presets array based on the spacing scale provided.
+	 *
+	 * @ticket 56467
+	 *
+	 * @dataProvider data_set_spacing_sizes_when_invalid
+	 */
+	public function test_set_spacing_sizes_when_invalid( $spacing_scale, $expected_output ) {
+		$this->expectNotice();
+		$this->expectNoticeMessage( 'Some of the theme.json settings.spacing.spacingScale values are invalid' );
+
+		$theme_json = new WP_Theme_JSON(
+			array(
+				'version'  => 2,
+				'settings' => array(
+					'spacing' => array(
+						'spacingScale' => $spacing_scale,
+					),
+				),
+			)
+		);
+
+		$theme_json->set_spacing_sizes();
+		$this->assertSame( $expected_output, _wp_array_get( $theme_json->get_raw_data(), array( 'settings', 'spacing', 'spacingSizes', 'default' ) ) );
+	}
+
+	/**
+	 * Data provider for spacing scale tests.
+	 *
+	 * @ticket 56467
+	 *
+	 * @return array
+	 */
+	function data_set_spacing_sizes_when_invalid() {
+		return array(
+
+			'invalid_spacing_scale_values_missing_operator' => array(
+				'spacingScale'    => array(
+					'operator'   => '',
+					'increment'  => 1.5,
+					'steps'      => 1,
+					'mediumStep' => 4,
+					'unit'       => 'rem',
+				),
+				'expected_output' => null,
+			),
+
+			'invalid_spacing_scale_values_non_numeric_increment' => array(
+				'spacingScale'    => array(
+					'operator'   => '+',
+					'increment'  => 'add two to previous value',
+					'steps'      => 1,
+					'mediumStep' => 4,
+					'unit'       => 'rem',
+				),
+				'expected_output' => null,
+			),
+
+			'invalid_spacing_scale_values_non_numeric_steps' => array(
+				'spacingScale'    => array(
+					'operator'   => '+',
+					'increment'  => 1.5,
+					'steps'      => 'spiral staircase preferred',
+					'mediumStep' => 4,
+					'unit'       => 'rem',
+				),
+				'expected_output' => null,
+			),
+
+			'invalid_spacing_scale_values_non_numeric_medium_step' => array(
+				'spacingScale'    => array(
+					'operator'   => '+',
+					'increment'  => 1.5,
+					'steps'      => 5,
+					'mediumStep' => 'That which is just right',
+					'unit'       => 'rem',
+				),
+				'expected_output' => null,
+			),
+
+			'invalid_spacing_scale_values_missing_unit' => array(
+				'spacingScale'    => array(
+					'operator'   => '+',
+					'increment'  => 1.5,
+					'steps'      => 5,
+					'mediumStep' => 4,
+				),
+				'expected_output' => null,
+			),
+		);
+	}
+
 	/**
 	 * @ticket 56467
 	 */
 	function test_get_styles_for_block_with_padding_aware_alignments() {
-		$theme_json = new WP_Theme_JSON_Gutenberg(
+		$theme_json = new WP_Theme_JSON(
 			array(
 				'version'  => 2,
 				'styles'   => array(
@@ -3378,7 +3713,7 @@ function test_get_styles_for_block_with_padding_aware_alignments() {
 	 * @ticket 56467
 	 */
 	function test_get_styles_for_block_without_padding_aware_alignments() {
-		$theme_json = new WP_Theme_JSON_Gutenberg(
+		$theme_json = new WP_Theme_JSON(
 			array(
 				'version' => 2,
 				'styles'  => array(
@@ -3409,7 +3744,7 @@ function test_get_styles_for_block_without_padding_aware_alignments() {
 	 * @ticket 56467
 	 */
 	function test_get_styles_for_block_with_content_width() {
-		$theme_json = new WP_Theme_JSON_Gutenberg(
+		$theme_json = new WP_Theme_JSON(
 			array(
 				'version'  => 2,
 				'settings' => array(