Photo Dimensions
Anyone taking pictures should be aware of the photo dimensions. 
Knowing the different sizes will ensure the print sizes come out all right.
Ratios
Majority of cameras today use the 3:2 ratio. What this means is the long side is 1.5x longer than the short end. This is the reason why the 4×6 has become something of a standard. When you examine the camera viewfinder, you will see this is the size used.
But if the ratios are not the same, the picture will have to be cropped. For example, if you print the image on a 5 x 7 or 8 x 10, the photo dimensions and ratio will differ.
The 5 x7 uses a 3.5:2.5 ratio. This means the long side is 1.4x the short side. The ratio for the 8 x 10 is 1.25x longer than the short end.
If you are taking pictures to be used as portraits, leave some extra space on the long side so nothing gets cropped.
Common Print Sizes
They are 4 x 6 (multiplication factor: 1.5), 5 x 7 (- 1.4), 8 x 10 (- 1.25), 10 x 13 (– 1.3), 10 x 20 (– 2), 16 x 20 (- 1.25), 20 x 24 (- 1.2) and 20 x 30 (- 1.5). There are however, others available.
Other Photo Dimensions and Specifications
Sometimes the photo prints are measured in millimeters. Here are some of the most common sizes and their equivalents.
3¼" × 4½ is equal to 82.5 × 120 mm (ratio: 16:11, 1.45). 3½" × 5" is equal to 89 × 127 mm (10:7, 1.43); 4" × 6" is the same as 102 × 152 mm (3:2, 1.5); 4½" × 6" size has no millimeter equivalent. Its aspect ratio is 4:3 (1.33). This size is relatively new and used in digital cameras.
5" × 7" is equal to 127 × 178 mm with an aspect ratio of 7:5 (1.4); 6" × 8" is the same as 152 × 203 mm (4:3, 1.33), while 8" × 10" is equal to 203 × 254 mm (5:4, 1.25). 8" × 12" is the same as 203 × 305 mm (3:2, 1.5).
The 10" × 12" photo dimensions are equal to 54 × 305 mm (6:5, 1.2). The 10" × 15" size is the same as 254 × 381 mm (3:2, 1.5); 11" × 14"is equal to 279 × 356 mm (14:11, 1.27), and 11" × 17" is the same as 279 × 432 mm (17:11, 1.54).
The 12" × 15" size is equivalent to 305 × 381 mm (5:4, 1.25) and 12" × 18" is the same as 305 × 465 mm (3:2, 1.5).
Tips
Check the specs for the camera you are using. Because technology is always evolving, the photo specs of these devices are always changing.
Whether you are a professional photographer or not, being aware of the different photo dimensions will help you take better pictures. In addition, you also reduce the risks of getting that image cropped because the ratios do not match.
