Measuring 10x15cm, 4x6" 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 4x6", you'll need at least 288 x 432px and ideally 1200 x 1800px.
If you are looking for a frame with a mat for an 4x6" photo, choose the 8x10" (20x25cm) frame. The mat will have an 4x6" (10x15cm) opening.