diff --git a/src/mdevaluate/coordinates.py b/src/mdevaluate/coordinates.py
index 6711508..722ca5b 100755
--- a/src/mdevaluate/coordinates.py
+++ b/src/mdevaluate/coordinates.py
@@ -232,7 +232,7 @@ class Coordinates:
         return sliced
 
     def __len__(self):
-        return len(self.frames)
+        return len(self.frames[self._slice])
 
     def __checksum__(self):
         return checksum(self.frames, self.atom_filter, self._slice, self.mode)