diff --git a/ql/src/codeql/files/FileSystem.qll b/ql/src/codeql/files/FileSystem.qll
index 372a53b53c0..d9da4d01cac 100644
--- a/ql/src/codeql/files/FileSystem.qll
+++ b/ql/src/codeql/files/FileSystem.qll
@@ -190,4 +190,7 @@ class File extends Container, @file {
 
   /** Gets the number of lines of comments in this file. */
   int getNumberOfLinesOfComments() { result = count(int line | this.line(line, true)) }
+
+  /** Holds if this file was extracted from ordinary source code. */
+  predicate fromSource() { files(this, _, _, _, 1) }
 }
diff --git a/ql/src/queries/summary/LinesOfUserCode.ql b/ql/src/queries/summary/LinesOfUserCode.ql
new file mode 100644
index 00000000000..c7dbb7ee5ba
--- /dev/null
+++ b/ql/src/queries/summary/LinesOfUserCode.ql
@@ -0,0 +1,17 @@
+/**
+ * @id rb/summary/lines-of-user-code
+ * @name Lines of authored Ruby code in the database
+ * @description The total number of lines of Ruby code across files, excluding library and generated code.
+ * @kind metric
+ * @tags summary
+ */
+
+import ruby
+
+select sum(File f |
+    f.fromSource() and
+    exists(f.getRelativePath()) and
+    not f.getAbsolutePath().matches("%/vendor/%")
+  |
+    f.getNumberOfLinesOfCode()
+  )