diff --git a/grum/mdi/mdisubwin.py b/grum/mdi/mdisubwin.py
index 64c45a1..03c5518 100644
--- a/grum/mdi/mdisubwin.py
+++ b/grum/mdi/mdisubwin.py
@@ -4,12 +4,17 @@ from PyQt5.QtWidgets import QMdiSubWindow
 from .. import assets
 
 
+SUB_WIN_WIDTH  = 640
+SUB_WIN_HEIGHT = 480
+
+
 class MDISubWindow(QMdiSubWindow):
 
     def __init__(self, title, *args, **kwargs):
         super().__init__(*args, **kwargs)
         self.setWindowTitle(title)
         self.setWindowIcon(assets.char())
+        self.resize(SUB_WIN_WIDTH, SUB_WIN_HEIGHT)
 
         # without this, the SubWindow is not removed from the subWindowList
         self.setAttribute(Qt.WA_DeleteOnClose)