This is because a standard photo size allows for easier frame selection as it has a large number of options available. The most common sizes for personal photos and decorative displays are the familiar 4x6, 5x7 and 8x10, according to Visuals Clipping. The standard size option will also minimize the need for custom framing. Before buying a frame, it is crucial to know the actual opening size since the opening size will vary depending on the type of mat, border and style of frame.