4×6 photos are basically just what they sound like: four inches by six inches. However, there are definitely some caveats.
Digital photos cropped to fit a 4×6 print
A modern phone camera like an iPhone or an Android produces photos that are not the same shape as a 4×6 photo. To make your photo fit on a 4×6 print, the top, bottom, left or right (or all edges) of your photo will need to be cropped.
The shape of the photo is called the aspect ratio or ratio. For instance, the aspect ratio of a 4×6 photo is 3:2.
Getting photos cropped for print has long been a problem.
check below example
The faces in my photos were cut off at the edge! Why?
The most obvious gotcha with printing 4×6 photos is that the photo printers cut off an extra 3 millimeters (0.12 inches) from each side of the image. CVS and Walgreens have the same problem. Neither the upload and crop interfaces make this information clear. It happens just after your photos have been printed, when the photo machine cuts them! You never want to show up at Walgreens with photos where everyone’s faces are cut off, even when you painstakingly cropped them before sending them off for printing. In general, you should place faces and other important objects far enough away from the edge of your image.
The majority of printers trim an additional 3 millimeters (0.12 inches) off a 4×6 image when it is printed, as shown in this red border.
New 4×4 format
Many photo printers are now capable of printing 4′′x4′′ squares. Printing photos on Instagram has never been easier with this cool new format.