Measuring 25x40cm, 10x16" 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 10x16", you'll need at least 720 x 1152px and ideally 3000 x 4800px.
If you are looking for a frame with a mat for an 10x16" photo, choose the 14x20" (35x48cm) frame. The mat will have an 10x16" (25x40cm) opening.