An Introduction to Aspect Ratio Shapes Used in Photography

=== by Bob Sutherland ===

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Have you ever wondered why the shape of photographs and the shape of computer screens are not the same? This is a lesson about aspect ratios and photo shapes.

If you enjoy working with numbers then you will be happy to discover that there are lots of opportunities for making measurements and using your mathematics skills when doing photography. One of those measurements is aspect ratios.

Definition: aspect ratio is a comparison of the lengths of the straight sides of a polygon. It is usually written as a ratio.

length side 1 : length side 2 : length side 3 : length side 4 : length side 5

For example: a triangle, square, rectangle, pentagon (5 sides), hexagon (6 sides) and octagon (8 sides) all have straight sides. They are all examples of polygons. A polygon is any straight sided shape that has three or more sides.

The aspect ratio of a square and a rectangle is:

length of the width : length of the height = width : height

Photographs are often printed on six inch by four inch sheets of photographic paper. The photograph is a rectangle measuring 6" x 4". The aspect ratio is therefore 6:4 when the photograph is in landscape orientation or 4:6 in portrait orientation.

135 film is commonly referred to 35 mm film. The total width of the film (including the strips containing the sprocket holes along each side) measures 35 millimetres across. Each picture frame on the film measures 36 mm by 24 mm. The picture frame has an aspect ratio of 36:24 .

You can, and usually should, simplify an aspect ratio to the smallest numbers that are in the same proportion. It is the same process as simplifying a fraction.

36 and 24 can both be divided by 12.

36:24 = 36/12 : 24/12 = 3:2

6 and 4 can both be divided by 2.

6:4 = 6/2 : 4/2 = 3:2

1080:720 = 1080/360 : 720/360 = 3:2

1200:800 = 1200/400 : 800/400 = 3:2

1536:1024 = 1536/512 : 1024/512 = 3:2

1920:1280 = 1920/640 : 1280/640 = 3:2

35 mm film has been around for approximately 90 years and was commonly used for at least half a century. Being well rooted in this long tradition 3:2 has become one of the dominant aspect ratios you will frequently encounter in photography.

Another dominant aspect ratio is 4:3. Many of the cathode ray tube television and computer monitors from the 1950's to the early 2000's had screens in the ratio of four units wide by three units high. The manufacturers and stores advertised the screens based on their diagonal measurement from bottom left corner to top right corner. The diagonal measurements could change from one model to another as screens gradually got bigger but their shape and aspect ratio remained constant at 4:3.

A common screen size among the computers in my computer lab during the late 1990's to early 2000's was 800 pixels wide by 600 pixels high.

800:600 = 800/200 : 600/200 = 4:3

1200:900 = 1200/300 : 900/300 = 4:3

1280:960 = 1280/320 : 960/320 = 4:3

1920:1440 = 1920/480 : 1440/480 = 4:3

A square is a common shape in photography. Many of my family's ancient photos from the 1880's to 1970 were taken with film cameras and printed as squares.

The width and height of a square are equal. Therefore the aspect ratio of a square is always 1:1 .

16:9 is a common aspect ratio for thin, wide screen televisions and desktop computer monitors. Modern videos often use a 16:9 aspect ratio.

1280:720 = 1280/80 : 720/80 = 16:9

1920:1080 = 1920/120 : 1080/120 = 16:9

16:10 = 8:5 is sometimes used as an alternative to 16:9 for devices such as laptop computer screens.

1280:800 = 1280/160 : 800/160 = 8:5

1920:1200 = 1920/240 : 1200/240 = 8:5

A very wide assortment of pixel dimensions and aspect ratios have appeared in the marketplace for smartphone screens. Tablets screens often have an aspect ratio that matches or is close to 2:3 , 3:4 , 5:8 or 9:16 .

The camera of your smartphone, tablet or digital camera probably has a menu that lets you choose the aspect ratio before taking a photograph. Common aspect ratios for digital photos are square 1:1 , 3:2 , 4:3 and 16:9 .