sashippers
Hi
The total size id divided in 12 grid in Bootstrap
Sidebar using 3,3 and Mainbody 6 columns.
If you want to customize the grid size, you can change it from template folder/tpls/blocks/mainbody/two-sidebar.php file
Please note : If you increase size of sidebars, it will required to decrease mainbody size, as total size must be 12.