Measuring 29x42cm, 11.69x16.54" is a common size for photo prints, art work and posters. The standard way to measure a print is by measuring width by height.
To get the best print result for 11.69x16.54", you'll need at least 841 x 1190px and ideally 3507 x 4962px.
If you are looking for a frame with a mat for an 11.69x16.54" photo, choose the 15x20" (38x48cm) frame. The mat will have an 11.69x16.54" (29x42cm) opening.