diff --git a/Firestore/core/src/firebase/firestore/util/filesystem.h b/Firestore/core/src/firebase/firestore/util/filesystem.h
index bef66137beb..fcbf51fc886 100644
--- a/Firestore/core/src/firebase/firestore/util/filesystem.h
+++ b/Firestore/core/src/firebase/firestore/util/filesystem.h
@@ -21,6 +21,7 @@
 
 #include "Firestore/core/src/firebase/firestore/util/path.h"
 #include "Firestore/core/src/firebase/firestore/util/status.h"
+#include "Firestore/core/src/firebase/firestore/util/statusor.h"
 
 namespace firebase {
 namespace firestore {
@@ -72,6 +73,12 @@ Status RecursivelyDelete(const Path& path);
  */
 Path TempDir();
 
+/**
+ * On success, returns the size in bytes of the file specified by
+ * `path`.
+ */
+StatusOr<off_t> FileSize(const Path& path);
+
 /**
  * Implements an iterator over the contents of a directory. Initializes to the
  * first entry in the directory.
diff --git a/Firestore/core/src/firebase/firestore/util/filesystem_posix.cc b/Firestore/core/src/firebase/firestore/util/filesystem_posix.cc
index 6d3048f45bf..a8040cbd873 100644
--- a/Firestore/core/src/firebase/firestore/util/filesystem_posix.cc
+++ b/Firestore/core/src/firebase/firestore/util/filesystem_posix.cc
@@ -95,6 +95,16 @@ Path TempDir() {
 }
 #endif  // !defined(__APPLE__)
 
+StatusOr<off_t> FileSize(const Path& path) {
+  struct stat st {};
+  if (stat(path.c_str(), &st) == 0) {
+    return StatusOr<off_t>(st.st_size);
+  } else {
+    return StatusOr<off_t>(Status::FromErrno(
+        errno, StringFormat("Failed to stat file: %s", path.ToUtf8String())));
+  }
+}
+
 namespace detail {
 
 Status CreateDir(const Path& path) {
diff --git a/Firestore/core/test/firebase/firestore/util/filesystem_test.cc b/Firestore/core/test/firebase/firestore/util/filesystem_test.cc
index 7dba108db0e..98b3924d1dd 100644
--- a/Firestore/core/test/firebase/firestore/util/filesystem_test.cc
+++ b/Firestore/core/test/firebase/firestore/util/filesystem_test.cc
@@ -45,6 +45,15 @@ static Path TestFilename() {
   return Path::FromUtf8("firestore-testing-" + CreateAutoId());
 }
 
+static void WriteBytesToFile(const Path& path, int byte_count) {
+  std::string bytes(byte_count, 'a');
+  std::ofstream out{path.native_value()};
+  ASSERT_TRUE(out.good());
+  out << bytes;
+  out.close();
+  ASSERT_TRUE(out.good());
+}
+
 #define ASSERT_NOT_FOUND(expression)                              \
   do {                                                            \
     ASSERT_EQ(FirestoreErrorCode::NotFound, (expression).code()); \
@@ -236,6 +245,22 @@ TEST(FilesystemTest, RecursivelyDeletePreservesPeers) {
   EXPECT_OK(RecursivelyDelete(root_dir));
 }
 
+TEST(FilesystemTest, FileSize) {
+  Path file = Path::JoinUtf8(TempDir(), TestFilename());
+  ASSERT_NOT_FOUND(FileSize(file).status());
+  Touch(file);
+  StatusOr<off_t> result = FileSize(file);
+  ASSERT_OK(result.status());
+  ASSERT_EQ(0, result.ValueOrDie());
+
+  WriteBytesToFile(file, 100);
+  result = FileSize(file);
+  ASSERT_OK(result.status());
+  ASSERT_EQ(100, result.ValueOrDie());
+
+  EXPECT_OK(RecursivelyDelete(file));
+}
+
 }  // namespace util
 }  // namespace firestore
 }  // namespace firebase