300 dpi means 300 dots every inch.

a 12" wide print will be 12 X 300 = 3600 dots wide.

a 12" x 10" print will be made up of 3600 X 3000 dots.

A 13" X 19" print will be 13 X 300 = 3900 dots wide. It will be 3900 X 5700 dots altogether.