Whether for photo, video or web: the aspect ratio decides whether an image fits the frame or looks distorted. With the Aspect Ratio & Image Scaling Calculator you determine the ratio and calculate any missing dimension proportionally. This post explains the basics and the math behind it.
What is aspect ratio?
The aspect ratio describes the width in relation to the height, written as width:height. It is independent of the absolute pixel count: an image with a width of 1920 pixels and a height of 1080 pixels has the same ratio as an image of 1280 × 720 pixels. To get from absolute dimensions to the compact ratio, you divide by the greatest common divisor (GCD). For 1920:1080 the GCD is 120, which yields 16:9.
Scaling proportionally without distortion
When scaling, the ratio is only preserved if both edges are multiplied by the same factor. If you set a new width, the new height follows from the formula: new height = old height × (new width ÷ old width). Conversely, for a given height: new width = old width × (new height ÷ old height). If the new dimensions deviate from the factor, the image is squeezed or stretched.
Example: scaling 1920 × 1080 to 1280
Source image: 1920 × 1080 pixels, ratio 16:9. Desired new width: 1280 pixels. The factor is 1280 ÷ 1920 = 0.6667. The new height is 1080 × 0.6667 = 720 pixels. The result 1280 × 720 keeps exactly the 16:9 ratio – the image stays undistorted. The calculator handles this exact computation as soon as you enter the original size and one new edge.
Common aspect ratios
A few ratios have become standard in photo, video and web. The table below shows typical uses:
| Ratio | Typical use |
|---|---|
| 16:9 | HD/UHD video, monitors, TV |
| 16:10 | notebook and studio displays |
| 4:3 | older monitors, classic photos |
| 3:2 | DSLR and mirrorless cameras |
| 21:9 | cinema ultrawide, film format |
| 1:1 | square, social media posts |
Knowing these ratios lets you pick the right format when cropping and exporting and avoids letterboxing or distortion.
