diff --git a/b2mirror/mirror.py b/b2mirror/mirror.py
index 52fcc5a..2108160 100644
--- a/b2mirror/mirror.py
+++ b/b2mirror/mirror.py
@@ -29,7 +29,7 @@ Dest will upload the file, and inform the manager it was completed
 
 class B2SyncManager(object):
 
-    def __init__(self, source_module, dest_module, exclude_res=None, workers=10):
+    def __init__(self, source_module, dest_module, exclude_res=None, workers=10, compare_method="mtime"):
         """
         :param source_module: subclass instance of b2mirror.base.Provider acting as a file source
         :param dest_module: subclass of b2mirror.base.Receiver acting as a file destination
@@ -45,11 +45,17 @@ class B2SyncManager(object):
         self.exclude_res = [
             re.compile(r'.*\.(DS_Store|pyc|dropbox)$'),
             re.compile(r'.*__pycache__.*'),
-            re.compile(r'.*\.dropbox\.cache.*')
+            re.compile(r'.*\.dropbox\.cache.*'),
+            re.compile(r'.*\.AppleDouble.*')
         ] + (exclude_res if exclude_res else [])
         self.workers = workers
         self._init_db()
 
+        self.should_transfer = {
+            "mtime": self._should_transfer_mtime,
+            "size": self._should_transfer_size
+        }[compare_method]
+
     @staticmethod
     def dict_factory(cursor, row):
         d = {}
@@ -141,7 +147,10 @@ class B2SyncManager(object):
 
         row = c.execute("SELECT * FROM 'files' WHERE `path` = ?;", (f.rel_path,)).fetchone()
 
-        if not row or row['mtime'] < f.mtime:
+        if self.should_transfer(row, f):
+
+            # The file was uploaded, commit it to the db
+            c.execute("REPLACE INTO 'files' VALUES(?, ?, ?, ?);", (f.rel_path, f.mtime, f.size, 1))
 
             print("Uploading:", f.rel_path)
             try:
@@ -150,11 +159,6 @@ class B2SyncManager(object):
                 print("Failed:", f.rel_path)
                 print("Unexpected error:", sys.exc_info()[0])
                 raise
-            # print("Ok: ", f.rel_path)
-
-            # The file was uploaded, commit it to the db
-            c.execute("REPLACE INTO 'files' VALUES(?, ?, ?, ?);", (f.rel_path, f.mtime, f.size, 1))
-            # print("Done: ", f.rel_path)
 
         else:
             c.execute("UPDATE 'files' SET seen=1 WHERE `path` = ?;", (f.rel_path,)).fetchone()
@@ -165,6 +169,12 @@ class B2SyncManager(object):
 
         return result
 
+    def _should_transfer_mtime(self, row, f):
+        return not row or row['mtime'] < f.mtime
+
+    def _should_transfer_size(self, row, f):
+        return not row or row['size'] != f.size
+
     def purge_remote(self):
         """
         Delete files on the remote that were not found when scanning the local tree.
@@ -181,7 +191,7 @@ class B2SyncManager(object):
         c.close()
 
 
-def sync(source_uri, dest_uri, account_id, app_key, workers=10, exclude=[]):
+def sync(source_uri, dest_uri, account_id, app_key, workers=10, exclude=[], compare_method="mtime"):
     source = urlparse(source_uri)
     dest = urlparse(dest_uri)
 
@@ -202,5 +212,5 @@ def sync(source_uri, dest_uri, account_id, app_key, workers=10, exclude=[]):
     assert source_provider is not None
     assert dest_receiver is not None
 
-    syncer = B2SyncManager(source_provider, dest_receiver, workers=workers, exclude_res=exclude)
+    syncer = B2SyncManager(source_provider, dest_receiver, workers=workers, exclude_res=exclude, compare_method=compare_method)
     syncer.sync()
diff --git a/bin/b2mirror b/bin/b2mirror
index 9017827..6a10d47 100755
--- a/bin/b2mirror
+++ b/bin/b2mirror
@@ -9,6 +9,7 @@ from b2mirror import mirror
 def main():
     parser = argparse.ArgumentParser(description="Sync data to/from B2")
 
+    parser.add_argument("-i", "--size", help="Compare by size instead of mtime", action="store_true", default=False)
     parser.add_argument("-w", "--workers", help="Maximum parallel uploads", type=int, default=10)
 
     parser.add_argument("-s", "--source", required=True, help="Source URI")
@@ -17,13 +18,21 @@ def main():
     parser.add_argument("-a", "--account-id",   required=True, help="Backblaze account ID")
     parser.add_argument("-k", "--app-key",   required=True, help="Backblaze application key")
 
-    parser.add_argument("--exclude", nargs="+", help="Regexes to exclude from transfer")
+    parser.add_argument("--exclude", nargs="+", help="List of regexes to exclude from transfer")
 
     args = parser.parse_args()
 
     ignore_res = [re.compile(i) for i in args.exclude]
 
-    mirror.sync(args.source, args.dest, args.account_id, args.app_key, workers=args.workers, exclude=ignore_res)
+    mirror.sync(
+        args.source,
+        args.dest,
+        args.account_id,
+        args.app_key,
+        workers=args.workers,
+        exclude=ignore_res,
+        compare_method="size" if args.size else "mtime"
+    )
 
 if __name__ == '__main__':
     main()