For some reason, printer resolution is universally measured in dots per inch, even though, outside of the U.S. paper sizes a measured in metric units.

Fortunately the software that is used for resampling does all the conversions for us, so except for learning purposes, there's no need to have to convert metric paper sizes into inches to find out how many dots will be on our printed photo.

For an explanation of why we can think of a Canon printer as having a 'native' resolution of 300 dpi see this page.