An aspect ratio is the proportional relationship between an image or video’s width and height. It is usually written as width:height, such as 16:9 for widescreen or 9:16 for vertical video. Knowing the ratio helps you resize content without stretching it and decide whether a crop is needed for a different layout.
To calculate a ratio from pixel dimensions, simplify the width and height by dividing both by their greatest common divisor. To calculate a matching dimension, preserve the width-to-height proportion.
Need an instant result? Use the Cliperfly aspect ratio calculator to identify a ratio and calculate a matching height.
Formula 1: calculate an aspect ratio from dimensions
Simplified ratio = (width ÷ GCD) : (height ÷ GCD)
For a 1920 × 1080 video, the greatest common divisor is 120. Divide both dimensions by 120 and the ratio becomes 16:9. For a 1080 × 1920 vertical video, dividing both values by 120 gives 9:16.
Worked examples
| Pixel dimensions | Simplified ratio | Shape |
|---|---|---|
| 1920 × 1080 | 16:9 | Landscape |
| 1080 × 1920 | 9:16 | Portrait |
| 1080 × 1080 | 1:1 | Square |
| 1200 × 1500 | 4:5 | Portrait |
| 1600 × 1200 | 4:3 | Landscape |
Formula 2: calculate a matching height
If you know the width and height of the original and want a new width, the matching height is:
For a 16:9 frame that is 1280 pixels wide, the matching height is 1280 × 9 ÷ 16 = 720 pixels. The result is 1280 × 720, still a 16:9 frame.
Formula 3: calculate a matching width
If you know the target height instead, use:
For a 9:16 frame at 1920 pixels high, the matching width is 1920 × 9 ÷ 16 = 1080 pixels.
Common aspect ratios
| Ratio | Example resolution | Common application |
|---|---|---|
| 9:16 | 1080 × 1920 | Vertical short-form video |
| 16:9 | 1920 × 1080 | Widescreen video |
| 1:1 | 1080 × 1080 | Square image or video |
| 4:5 | 1080 × 1350 | Portrait social image |
| 4:3 | 1440 × 1080 | Classic photo or display |
These dimensions are examples, not guarantees of a platform’s latest requirements. Always check the destination’s current guidance before preparing a large batch of content.
Aspect ratio is not the same as resolution
Resolution describes the number of pixels in an image. Aspect ratio describes its shape. For instance, 1280 × 720 and 1920 × 1080 are different resolutions but both have a 16:9 ratio. You can reduce dimensions while preserving the ratio, but resizing cannot create detail that is not in the original file.
When should you crop instead of resize?
Resize proportionally when the destination supports your existing ratio. Crop when a layout requires a different shape and it is acceptable to remove part of the image. Avoid stretching to force a mismatch, because stretching changes the shape of people and objects.
To inspect a local photo’s dimensions and preview a centered crop, use the Image Aspect Ratio Checker. It processes the selected image in the browser rather than uploading it to the site.
Frequently asked questions
How do I calculate an aspect ratio manually?
Write width:height, then divide both numbers by their greatest common divisor to simplify. For 1920:1080, divide both by 120 to get 16:9.
How do I calculate the height for a 16:9 video?
Multiply the new width by 9 and divide by 16. For 1280 pixels wide, 1280 × 9 ÷ 16 = 720 pixels high.
Can aspect ratio be a decimal?
Yes. Dividing width by height produces a decimal ratio. The colon format such as 16:9 is commonly used because it expresses the same relationship with two numbers.
Will preserving aspect ratio stop cropping?
It stops the image from being stretched when resized, but it does not guarantee that a destination layout will not crop it. If the target ratio differs from the source, the destination may crop or add empty space.
Calculate a ratio with your own dimensions.
Use the aspect ratio calculator