If you choose 72 dpi, then 2340 pixels is 2340 / 72 = 32.5 inches, which is approximately 85.8 cm. (2.54 cm per inch, if I recall correctly). At 300 dpi, then 2340 pixels is 2340 / 300 = 7.8 inches, or 19.8 cm.

Changing the dpi changes the visual quality and size of the image when it's printed. The closer the dots are to one another, the better the colors blend together and the sharper the image can appear (to a point—your paper must be able to bear the load of the ink). Choose the print resolution based on the distance you anticipate the viewer being from the page. If it's something they're going to hold in their hands, 300 dpi is a good starting point. 600 is good for gallery quality prints. 120 is pretty good for a poster. A billboard might be as low as 30 dpi because it's meant to be viewed from very far away.

But in summation:

pixels / dpi = physical size
pixels / size = dpi
dpi * size = pixels