diff --git a/pytiled_parser/common_types.py b/pytiled_parser/common_types.py
index c560bdb..c26c5a1 100644
--- a/pytiled_parser/common_types.py
+++ b/pytiled_parser/common_types.py
@@ -18,8 +18,8 @@ class Size(NamedTuple):
     """Size NamedTuple.
 
     Attributes:
-        width: The width of the object.
-        height: The height of the object.
+        width: The width of the object in pixels.
+        height: The height of the object in pixels.
     """
 
     width: float