Freestanding calendar size and design are optional.
The choice of format should be close to the standard sizes:

A standard printing formats:
A6 – 105x145 mm
A5 – 145x210 mm
A4 – 210x297 mm
A3 – 297x420 mm
A2 – 420x594 mm

B used in printing formats:
B4 – 243x350 mm
B5 – 175x243 mm
B6 – 120x175 mm
B7 – 85x120 mm

The size, color, thickness of the paper and technological additions (UV varnishing, cutting, gravure) can be freely chosen.
For Press release prepare files as for final page size, plus 2 mm bleeds at edges for trimming.