Aspect Ratio Explained: 16:9, 4:3, 3:2 and How to Resize Without Distortion

An aspect ratio is the relationship between width and height. It describes a shape, not a size: a phone screen and a cinema screen can share the same 16:9 aspect ratio even though one is a thousand times larger. Knowing the ratio lets you resize images, crop photos and choose screens without anything looking squashed.

Common aspect ratios

Ratio	As a decimal	Typical use
1:1	1.00	Square social media posts, profile photos
4:3	1.33	Older TVs and monitors, many tablets, phone cameras
3:2	1.50	35 mm film and many DSLR and mirrorless cameras
16:10	1.60	Many laptop screens
16:9	1.78	HD and 4K TVs, most online video
21:9	about 2.33	Ultrawide monitors (marketing name; actual ratios vary)
9:16	0.56	Vertical phone video and stories

Finding a missing width or height

height = width × (ratio height ÷ ratio width)
width = height × (ratio width ÷ ratio height)

A 16:9 video that must be 1,280 pixels wide is 1,280 × 9 ÷ 16 = 720 pixels tall. A 4:5 portrait image 1,350 pixels tall is 1,350 × 4 ÷ 5 = 1,080 pixels wide. You can do this with the solve mode of the ratio calculator: enter 16 : 9 = 1280 : ? and leave the last box empty.

Finding the aspect ratio of a resolution

Simplify the width and height by their greatest common factor. 1920 × 1080: the GCF is 120, giving 16 : 9. 2560 × 1600: the GCF is 320, giving 8 : 5, which is usually written as 16 : 10. Some resolutions don't simplify to neat numbers; 1366 × 768 reduces to 683 : 384, which is marketed as 16:9 because it is very close (1.779 vs 1.778).

Common 16:9 resolutions

Name	Resolution
HD	1280 × 720
Full HD	1920 × 1080
QHD	2560 × 1440
4K UHD	3840 × 2160

Resizing without distortion

Stretching happens when width and height change by different factors. To resize safely, scale both by the same factor, or lock the aspect ratio in your editing software. If the target shape is different, you have two honest choices:

Crop: cut part of the image to reach the new ratio. A 3:2 photo becomes 4:5 by trimming the sides.
Letterbox or pillarbox: fit the whole image and fill the leftover space with bars or a background.

Screen size and aspect ratio

Screens are sold by diagonal size, so two 27-inch screens with different ratios have different widths and heights. For a 16:9 screen, the diagonal is √(16² + 9²) ≈ 18.36 units; a 27-inch screen is therefore about 27 × 16 ÷ 18.36 = 23.5 inches wide and 27 × 9 ÷ 18.36 = 13.2 inches tall.

Printing photos

A 4 × 6 inch print is 2:3, which matches most camera sensors. An 8 × 10 print is 4:5, so a 3:2 photo has to be cropped. That's why prints sometimes cut off the edges of a picture you framed carefully. Check the ratio before ordering prints, or choose sizes such as 8 × 12 that keep 2:3.