Photo labs usually recommend the 4x6 size because - quite simply - its the universal format. When people ask how big is a photo 4x6 , the answer is 4 by 6 inches - which just happens to be the default setting for most printers. At Visuals Clipping
, printing pros explain that this size is great because it reduces waste and makes sure the colours come out perfectly. Its also super fast, super cheap and matches the 3:2 aspect ratio of most digital photos.