This is dependent on the amount of clearance you have on at least one side of your doorway. If you have enough clearance on one side, then the formula to calculate track length is [doorway width + width of 1 door]. So if your doorway is 60" wide and you are using two 36" wide doors, then you would want to order an 8' track [60" + 36" = 96"]. If you don’t have any/much clearance on either side of your doorway, then just order the kit with the longest track you will be able to fit for your installation (width of doorway + right side clearance + left side clearance). This allows you to maximize your access to the doorway by pushing the doors as far as they will go to one side of the doorway, when accessing the other side of the doorway. If you only want to extend the track to one side of your doorway, then just include the clearance measurement of that side. You can also use the "Track Lenth Calculator" found above the "Quantity" selector on the product page.