Every passepartout has two sizes, and the size we give you always tells you what it fits:
Outer size = the frame it fits. The outer size matches the frame size. A 70x100 cm passepartout fits a 70x100 cm frame.
Inner size (the window) = the poster it fits. The inner size is the size of the poster the passepartout is made for. A passepartout with a 50x70 cm window is made for a 50x70 cm poster.
On our product pages the size is written as the frame size, followed by the window size, for example 70x100 cm (window 50x70 cm). This passepartout fits a 70x100 cm frame and a 50x70 cm poster.
The window is cut slightly smaller than the poster, so the edges of the poster are covered. This means a passepartout with a 30x40 cm window is the right one for a 30x40 cm poster.