An aspect ratio is the width of an image to its height. Below we list the most common aspect ratios used in digital photography and what they refer to.
4:3 - The standard aspect ratio used in digital compact cameras, and Four Thirds cameras. This results in a slightly squarer image than that from most DSLRs; for this reason, it is best to print on a size matching the ratio, such as 8x6in. For print sizes such as A4 you'll have to crop the image, or trim the print.
3:2 - Most DSLRs, and some high-end compacts such as Sigma's DP range and some models from Ricoh's GX series, produce 3:2 ratio images as standard. This is the same aspect ratio as a frame of 35mm fi lm, and fi ts onto standard 6x4in prints without any cropping.
16:9 - The format now commonly used for widescreen capture in both video and stills. Cameras offer a 16:9 ratio by shielding parts from the top and bottom of a sensor, which comes at the slight expense of total resolution as those sections no longer capture information. The exception to this is the first Panasonic LX series compacts, which, unusually, featured 16:9 sensors.
6:6 / 1:1 - The square format, reminiscent of medium format film and available as an option on some cameras.