Measuring 60x60cm, 24x24" 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 24x24", you'll need at least 1728 x 1728px and ideally 7200 x 7200px.
If you are looking for a frame with a mat for an 24x24" photo, choose the 28x28" (70x70cm) frame. The mat will have an 24x24" (60x60cm) opening.