I'm holding a contest where people design a card and I will use the design to print it out and make a birthday card.

The site to make the card says the card will be 16,6 x 12 cm (16,6 height 12 width)

What size (in pixels) for the design is the best for this card?

In photoshop and illustrator you can input the size of the canvas in cm
however for print documents you want to use the cymk color scale and at least 150 dpi

i understand some of these words