Our printers print at 300 pixels per inch. So you can work out the best print size for your file by dividing the pixel width and height of the image by 300.
Eg. an image that is 3600 x 5400 is sized to print (3600/300) x (5400/300) = 12″ x 18″.
You can get a good indication of your print quality by viewing it on your computer at 100%. If you start to zoom in closer you will see the kind of quality you will get when you enlarge its print size.
Another thing to take into account is the distance of view for your print. See the example below – the image on the left has half the pixels of the one on the right which is why it looks like it has less definition. But as you move away from the two images the difference in image quality becomes a lot less obvious.
When images are saved for print it is important to make sure that the jpeg compression is set at its highest quality. Reducing the compression quality could result in images with compression banding and a loss of image sharpness.