What an aspect ratio is
The aspect ratio is the relation between width and height, written as two numbers with a colon. 1920 × 1080 divided by their largest common divisor, 120, gives 16:9, the shape of most screens and online videos. The calculator also shows the decimal form, 1.778:1, which is how cinema formats such as 2.39:1 are usually written, and names the nearest common ratio, so 1366 × 768 shows as close to 16:9 even though it reduces to 683:384.
Common ratios: 16:9 for HD and 4K video, YouTube and TV; 9:16 for vertical video such as Reels, TikTok and Shorts; 4:3 for older screens, iPad and many compact cameras; 3:2 for DSLR photos; 1:1 square and 4:5 portrait for Instagram posts; 21:9 for ultrawide monitors.
Resizing without distortion
To keep an image or video from being stretched, the new width and height must have the same ratio as the original. Type the new width and the height is calculated, or the other way round. For a 1920 × 1080 video at 1280 wide, the height is 720. The scale box does the same with a percentage: 50 percent of 4000 × 3000 is 2000 × 1500.
Most video encoders require even dimensions, so choose even pixels when the result is for a video. When the exact result is not a whole number, rounding changes the ratio by a tiny amount, and the calculator tells you. To actually resize or crop an image, use the image resizer or the crop tool linked below.