Index: clang-tidy/cppcoreguidelines/SlicingCheck.cpp
===================================================================
--- clang-tidy/cppcoreguidelines/SlicingCheck.cpp
+++ clang-tidy/cppcoreguidelines/SlicingCheck.cpp
@@ -122,11 +122,15 @@
       BaseDecl->getASTContext().getASTRecordLayout(BaseDecl);
   const auto &DerivedLayout =
       DerivedDecl->getASTContext().getASTRecordLayout(DerivedDecl);
-  const auto StateSize = DerivedLayout.getDataSize() - BaseLayout.getDataSize();
-  if (StateSize.isPositive()) {
+  const auto StateSizeInChars =
+      DerivedLayout.getDataSize() - BaseLayout.getDataSize();
+  if (StateSizeInChars.isPositive()) {
+    const int StateSizeInBits =
+        static_cast<int>(StateSizeInChars.getQuantity()) *
+        BaseDecl->getASTContext().getCharWidth();
     diag(Call->getExprLoc(), "slicing object from type %0 to %1 discards "
-                             "%2*sizeof(char) bytes of state")
-        << DerivedDecl << BaseDecl << static_cast<int>(StateSize.getQuantity());
+                             "%2 bits of state")
+        << DerivedDecl << BaseDecl << StateSizeInBits;
   }
 }
 
Index: test/clang-tidy/cppcoreguidelines-slicing.cpp
===================================================================
--- test/clang-tidy/cppcoreguidelines-slicing.cpp
+++ test/clang-tidy/cppcoreguidelines-slicing.cpp
@@ -31,18 +31,18 @@
 void positivesWithMemberVariables() {
   DerivedWithMemberVariables b;
   Base a{b};
-  // CHECK-MESSAGES: :[[@LINE-1]]:8: warning: slicing object from type 'DerivedWithMemberVariables' to 'Base' discards {{[0-9]*}}*sizeof(char) bytes of state [cppcoreguidelines-slicing]
+  // CHECK-MESSAGES: :[[@LINE-1]]:8: warning: slicing object from type 'DerivedWithMemberVariables' to 'Base' discards {{[0-9]*}} bits of state [cppcoreguidelines-slicing]
   a = b;
-  // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: slicing object from type 'DerivedWithMemberVariables' to 'Base' discards {{[0-9]*}}*sizeof(char) bytes of state
+  // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: slicing object from type 'DerivedWithMemberVariables' to 'Base' discards {{[0-9]*}} bits of state
   TakesBaseByValue(b);
-  // CHECK-MESSAGES: :[[@LINE-1]]:20: warning: slicing object from type 'DerivedWithMemberVariables' to 'Base' discards {{[0-9]*}}*sizeof(char) bytes of state
+  // CHECK-MESSAGES: :[[@LINE-1]]:20: warning: slicing object from type 'DerivedWithMemberVariables' to 'Base' discards {{[0-9]*}} bits of state
 
   TwiceDerivedWithNoMemberVariables c;
   a = c;
-  // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: slicing object from type 'TwiceDerivedWithNoMemberVariables' to 'Base' discards {{[0-9]*}}*sizeof(char) bytes of state
+  // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: slicing object from type 'TwiceDerivedWithNoMemberVariables' to 'Base' discards {{[0-9]*}} bits of state
 
   a = ReturnsDerived();
-  // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: slicing object from type 'DerivedWithMemberVariables' to 'Base' discards {{[0-9]*}}*sizeof(char) bytes of state
+  // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: slicing object from type 'DerivedWithMemberVariables' to 'Base' discards {{[0-9]*}} bits of state
 }
 
 void positivesWithOverride() {