diff --git a/pigeon_magnet_solver/board.py b/pigeon_magnet_solver/board.py
index 355037e..649c58a 100644
--- a/pigeon_magnet_solver/board.py
+++ b/pigeon_magnet_solver/board.py
@@ -28,9 +28,6 @@ class Board:
         else:
             return len(self.rows[0])
 
-    def __len__(self) -> int:
-        return self.height * self.width
-
     def __post_init__(self) -> None:
         # check char set
         chars = {c for c in "".join(self.rows)}
@@ -44,7 +41,7 @@ class Board:
 
         # check buttons
         assert all(
-            button in range(len(self))
+            button in range(self.height * self.width)
             for button in self.buttons
         ), "Invalid buttons!"