Size: Approximately 27 cm wide Approximately 31 cm long No gusset Shoulder strap width: 2.5 cm Shoulder strap length: Approximately 55 cm No interfacing is used on the back of the surface. It's a single layer of fabric. The shoulder strap is made long so it can be worn on the shoulder. An A4-sized notebook will fit. There is another pocket in addition to the smartphone pocket. Interfacing is used on the shoulder straps. Thank you for your understanding regarding the use of vintage fabric and handmade items.