Depending on the size and shape of your exisiting pet door you may need to adjust the cut out hole. Cut out dimensions for the Deluxe Aluminium Pet Door are as follows: SML: 202mm(W) x 283mm(H) MED: 257mm(W) x 361mm(H) LGE: 316mm(W) x 460mm(H) XL: 396mm(W) x 637mm(H)