Measuring 22x30cm, 9x12" 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 9x12", you'll need at least 648 x 864px and ideally 2700 x 3600px.
If you are looking for a frame with a mat for an 9x12" photo, choose the 13x16" (32x40cm) frame. The mat will have an 9x12" (22x30cm) opening.