Definition: Aspect Ratio

Definition: Aspect Ratio | Glossary entry

Definition: Aspect Ratio

The aspect ratio of an image is the proportion of the long side to the short side of the image. Normally it is expressed as the relationship between the Width:Height (eg: 16:9). The two are tied by this relationship so that no matter what the length of the long side the short side will be in the same proportion.

The example of 16:9 could be 16 inches to 9 inches. Alternatively it could be 1600mm by 900mm. In the case of a screen measuring 1920 pixels wide the height would be (1920 x 9)/16 = 1080 pixels.

In still-image photography a range of common ratios are in use as follows…

  • 1:1 – Square image format commonly used in medium format cameras using square format film.
  • 4:3 (1.33:1) Used by many point-and-shoot cameras, and some manufacturer/brand specific cameras.
  • 3:2 (1.5:1) The classic 35mm film format. Most DSLR image sensors follow very closely to this format although manufacturer/brand variations exist. The APS-C format (Canon) and DX format (Nikon) both exhibit simular aspect ratios to the 3:2 image format.
  • 16:9 (1.77:1) Rooted in the cinema, this aspect ratio has recently become associated with HDTV (High Definition Television). The format has become popular for cameras that also shoot HD video. Some DSLRs will shoot 16:9 as well as other formats for the aspect ratio.
  • 3:1 Also comes from the APS format (Advanced Photographic System film Camera – a Kodak standard in film cameras).

Over the history of display and image management there has been a wide variety of common image aspect ratios in many different media types. Some are given below…

  • 1.33:1 or 1.37:1 (4:3) Old television & computer monitor standard
  • 1.41:1 or 1:√2 ~1:1.4142, ISO 216 paper sizes (A4)
  • 1.5:1 (3:2) Classic 35 mm film
  • 1.6:1 (8:5) Credit cards are 85.6 × 54 mm which is ~1.59:1
  • 1.618:1 The golden ratio
  • 1.66:1 (5:3) A common European widescreen standard; native Super 16 mm film.
  • 1.77:1 or 1.78:1 (16:9) HD video standard
  • 1.85:1 A common US widescreen cinema standard
  • 2.39:1 or 2.40:1 A current widescreen cinema standard