Thank you for your inquiry regarding this item from Prime-Line Products. In reply to your question, the way that Prime-Line Products determines the handing of their hardware for patio sliding doors is by the "inside looking out". In other words, if when you're standing in the inside of the home and facing your patio door and the handle set is on your right hand side, then that's the handing of your sliding patio door. If facing your patio slider and your handle set is on your left hand side, then that's the handing of your door.
For additional questions regarding this item, or any other product manufactured by Prime-Line Products, please call their toll free number at (877) 649-9740, or contact them by email at firstname.lastname@example.org