via: http://www.dedoimedo.com/computers/ubuntu-unity-2d-resize-launcher.html

The configuration files are located under /usr/share/unity-2d/shell. You will need sudo to edit the files contained therein. You should also create a backup of all the files before making any changes. The simplest way to backup would be:

tar cvfz ~/Documents/unity-2d-shell-backup.tar.gz/usr/share/unity-2d/shell/*

Now, you can proceed to edit the files in any text editor. The paths listed below are all relative to the Unity 2D shell path above.

Shell.qml, change:

width: 65 to width: 50

common/IconTile.qml, change:

sourceSize.width: 48 to sourceSize.width: 32sourceSize.height: 48 to sourceSize.height: 32

launcher/LauncherList.qml, change:

property int tileSize: 54 to property int tileSize: 38property int selectionOutlineSize: 65 toproperty int selectionOutlineSize: 50

That would be all. Logout, log back in.