diff -ur VirtualBox-4.3.38.orig/src/VBox/Additions/x11/vboxvideo/vboxvideo.c VirtualBox-4.3.38/src/VBox/Additions/x11/vboxvideo/vboxvideo.c
--- VirtualBox-4.3.38.orig/src/VBox/Additions/x11/vboxvideo/vboxvideo.c	2016-07-22 07:40:25.677409695 +0300
+++ VirtualBox-4.3.38/src/VBox/Additions/x11/vboxvideo/vboxvideo.c	2016-07-22 07:41:57.897416430 +0300
@@ -1083,8 +1083,8 @@
             TRACE_LOG("cx=%u, cy=%u\n", cx, cy);
             xf86ScrnToScreen(pScrn)->width = cx;
             xf86ScrnToScreen(pScrn)->height = cy;
-            xf86ScrnToScreen(pScrn)->mmWidth = cx * 254 / 960;
-            xf86ScrnToScreen(pScrn)->mmHeight = cy * 254 / 960;
+            xf86ScrnToScreen(pScrn)->mmWidth = cx * 254 / (pScrn->xDpi * 10);
+            xf86ScrnToScreen(pScrn)->mmHeight = cy * 254 / (pScrn->yDpi * 10);
             adjustScreenPixmap(pScrn, cx, cy);
             vbvxSetSolarisMouseRange(cx, cy);
         }