Page size in cm

I need to create a page frame of size 21x26cm but I don’t understand how to convert it into pixel this measure …

anybody can help me?

thank you:)

Depending on how exact you need the measurement, you can use 595.28 x 737.07 for the frame size or 595 x 737.

No special magic, I just used an online converter from centimeters to pixels (and assumed you needed 72 ppi).