Your artwork needs to be in one of the following four sizes : Postcard A5 (14.81 x 21.01 centimeters or 5.8 x 8.3 inches) A4 (21 x 29.7 centimeters or 8.27 x 11.69 inches) A3 (29.7 x 42 cm, 11.69 x 16.53 inches)