Measuring 18x27cm, 7x11" 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 7x11", you'll need at least 504 x 792px and ideally 2100 x 3300px.
If you are looking for a frame with a mat for an 7x11" photo, choose the 11x15" (27x38cm) frame. The mat will have an 7x11" (18x27cm) opening.
