My window size is 30" x 30" I don't understand the pricing per running foot. I only want to order for this one window (30" x 30"). Can you help me order slightly bigger then this window so I can trim

The width of this film is 50 inches across the roll. That would cover one of your dimensions, so you would just then need to order 3 feet of length to cover the other dimension. Our films are sold by the foot, not the inch. This will enable you to have plenty for the install.