diff --git a/Detector/DetDriftChamber/compact/det.xml b/Detector/DetDriftChamber/compact/det.xml
index 58b3c68b7ba41b19e160d0795d2e093f495a699d..bfd81e73dea5721de9e4b9bbb16f0d25512b6d3b 100644
--- a/Detector/DetDriftChamber/compact/det.xml
+++ b/Detector/DetDriftChamber/compact/det.xml
@@ -19,7 +19,7 @@
 
 
   <define>
-    <constant name="world_size" value="30*m"/>
+    <constant name="world_size" value="2226*mm"/>
     <constant name="world_x" value="world_size"/>
     <constant name="world_y" value="world_size"/>
     <constant name="world_z" value="world_size"/>