Fix Project#update_repository_size to convert MB to Bytes properly

app/models/project_statistics.rb

@@ -25,8 +25,9 @@ class ProjectStatistics < ActiveRecord::Base
     self.commit_count = project.repository.commit_count
   end
 
+  # Repository#size needs to be converted from MB to Byte.
   def update_repository_size
-    self.repository_size = project.repository.size
+    self.repository_size = project.repository.size * 1.megabyte
   end
 
   def update_lfs_objects_size

changelogs/unreleased/26773-fix-project-statistics-repository-size.yml

@@ -0,0 +1,4 @@
+---
+title: Adjust ProjectStatistic#repository_size with values saved as MB
+merge_request: 8616
+author:

spec/models/project_statistics_spec.rb

@@ -107,7 +107,7 @@ describe ProjectStatistics, models: true do
 
   describe '#update_repository_size' do
     before do
-      allow(project.repository).to receive(:size).and_return(12.megabytes)
+      allow(project.repository).to receive(:size).and_return(12)
       statistics.update_repository_size
     end