diff --git a/changelog/fix_fix_layoutlinelength_reported_length.md b/changelog/fix_fix_layoutlinelength_reported_length.md
new file mode 100644
index 00000000000..bd50770a4fd
--- /dev/null
+++ b/changelog/fix_fix_layoutlinelength_reported_length.md
@@ -0,0 +1 @@
+* [#10078](https://github.com/rubocop/rubocop/pull/10078): Fix `Layout/LineLength` reported length when ignoring directive comments. ([@dvandersluis][])
diff --git a/lib/rubocop/cop/layout/line_length.rb b/lib/rubocop/cop/layout/line_length.rb
index cb50a69639e..47fa8c53d5f 100644
--- a/lib/rubocop/cop/layout/line_length.rb
+++ b/lib/rubocop/cop/layout/line_length.rb
@@ -183,8 +183,8 @@ def shebang?(line, line_index)
           line_index.zero? && line.start_with?('#!')
         end
 
-        def register_offense(loc, line, line_index)
-          message = format(MSG, length: line_length(line), max: max)
+        def register_offense(loc, line, line_index, length: line_length(line))
+          message = format(MSG, length: length, max: max)
 
           self.breakable_range = breakable_range_by_line_index[line_index]
 
@@ -241,9 +241,10 @@ def line_in_heredoc?(line_number)
         end
 
         def check_directive_line(line, line_index)
-          return if line_length_without_directive(line) <= max
+          length_without_directive = line_length_without_directive(line)
+          return if length_without_directive <= max
 
-          range = max..(line_length_without_directive(line) - 1)
+          range = max..(length_without_directive - 1)
           register_offense(
             source_range(
               processed_source.buffer,
@@ -251,7 +252,8 @@ def check_directive_line(line, line_index)
               range
             ),
             line,
-            line_index
+            line_index,
+            length: length_without_directive
           )
         end
 
diff --git a/spec/rubocop/cop/layout/line_length_spec.rb b/spec/rubocop/cop/layout/line_length_spec.rb
index 29eb59e098c..42dcaa6e5e9 100644
--- a/spec/rubocop/cop/layout/line_length_spec.rb
+++ b/spec/rubocop/cop/layout/line_length_spec.rb
@@ -345,7 +345,7 @@ def method_definition_that_is_just_under_the_line_length_limit(foo) # rubocop:di
       it 'highlights only the non-directive part' do
         expect_offense(<<~RUBY)
           #{'a' * 80}bcd # rubocop:enable Style/ClassVars
-          #{' ' * 80}^^^ Line is too long. [116/80]
+          #{' ' * 80}^^^ Line is too long. [83/80]
         RUBY
       end
 
@@ -353,7 +353,7 @@ def method_definition_that_is_just_under_the_line_length_limit(foo) # rubocop:di
         it 'highlights only the non-directive part' do
           expect_offense(<<~RUBY)
             #{'a' * 70} # bbbbbbbbbbbbbb # rubocop:enable Style/ClassVars'
-            #{' ' * 70}          ^^^^^^^ Line is too long. [121/80]
+            #{' ' * 70}          ^^^^^^^ Line is too long. [87/80]
           RUBY
         end
       end
@@ -362,7 +362,7 @@ def method_definition_that_is_just_under_the_line_length_limit(foo) # rubocop:di
         it 'registers an offense for the line' do
           expect_offense(<<-RUBY)
             LARGE_DATA_STRING_PATTERN = %r{\A([A-Za-z0-9\+\/#]*\={0,2})#([A-Za-z0-9\+\/#]*\={0,2})#([A-Za-z0-9\+\/#]*\={0,2})\z} # rubocop:disable Layout/LineLength
-            #{' ' * 68}^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Line is too long. [153/80]
+            #{' ' * 68}^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Line is too long. [117/80]
           RUBY
         end
       end