The 'format' of a film or camera is the dimensions of the image area (or frame).
- The 35mm (full-frame) film format used by stills cameras is 36 x 24mm.
- The 35mm (half-frame) format, used by motion-picture cameras is 24 x 18mm.
- The 2¼" square (medium) format is 57.15 x 57.15mm (not 60 x 60mm as is sometimes stated).
Format and Aspect Ratio are used interchangeably but are not exactly the same. Aspect Ratio is the ratio of horizontal to vertical dimensions of an image. (35mm slide frame is 3:2, TV 4:3, HDTV 16:9, 4X5 film 5:4)