The size includes the shelf.
These cushions are great! I deduct one star because the color is more of a dark olive green instead of dark gray as in the picture.
Basically, the seat cushion is OK, but something is wrong with the dimensions. 45X45cm never ever, it only comes to just under 39X39cm. If the all-round hem were added here, you still don't get the advertised size, it would be appropriate for the seat alone to be 45X45cm.
Super comfortable