diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index e232feaeada641a3930b11bb0909c68e833bae54..bbc01e9677c5b887220549f7f7ebe75d81ddac14 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -899,7 +899,8 @@ class MergeRequest < ActiveRecord::Base
   def compute_diverged_commits_count
     return 0 unless source_branch_sha && target_branch_sha
 
-    Gitlab::Git::Commit.between(target_project.repository.raw_repository, source_branch_sha, target_branch_sha).size
+    target_project.repository
+      .count_commits_between(source_branch_sha, target_branch_sha)
   end
   private :compute_diverged_commits_count
 
diff --git a/changelogs/unreleased/use-count_commits-directly.yml b/changelogs/unreleased/use-count_commits-directly.yml
new file mode 100644
index 0000000000000000000000000000000000000000..549e0744ea447ae8fe676d942f0220392a9b393c
--- /dev/null
+++ b/changelogs/unreleased/use-count_commits-directly.yml
@@ -0,0 +1,5 @@
+---
+title: Improve the performance for counting commits
+merge_request: 15628
+author:
+type: performance
diff --git a/lib/gitlab/git/repository.rb b/lib/gitlab/git/repository.rb
index d399636bb284651876b00c7afb15afdd7b392365..fb9c3e92d3f470372bce8efc6c995a165a1e8aa2 100644
--- a/lib/gitlab/git/repository.rb
+++ b/lib/gitlab/git/repository.rb
@@ -505,7 +505,7 @@ module Gitlab
 
       # Counts the amount of commits between `from` and `to`.
       def count_commits_between(from, to)
-        Commit.between(self, from, to).size
+        count_commits(ref: "#{from}..#{to}")
       end
 
       # Returns the SHA of the most recent common ancestor of +from+ and +to+