Here are some tips for resizing images for sending to an online photo-printing service:

 

Pixel Width and Height Limits. Printing requires much higher pixel dimensions than on-screen viewing, because photo printers have much higher resolution than computer screens. A good rule of thumb is to resize images with 200 pixels for each inch (80 pixels per cm), measured along the print's larger dimension. For example, to order a 5x7 inch (13x18 cm) print, use 7 x 200 = 1400 pixels. We recommend that you keep your width and height dimensions the same. This ensures that both horizontal and vertical images are resized to the same number of pixels per inch (cm) along their larger dimension. If you are ordering prints of 8x10 inches (20x27 cm) or larger, we recommend that you do not resize the images, unless your files are really large. You need to preserve the image quality of your original files.

 

File Format. The most popular format for printing photos is JPEG. You might want the higher image quality of the lossless PNG format, if the much larger files are acceptable, and your photo-printing service can accept the format.

 

File Size. With JPEG images, there is the usual trade-off between image quality and download speed (i.e. file size). As a general rule, you are more concerned with image quality than file size. In your resize settings, you should therefore specify a very high quality level of 95 or 97. If your photo printing service imposes a file size limit, use the settings option to specify a file size target equal to 10% below the maximum allowed.