Quick guide
How to use the Aspect Ratio Calculator
- Enter or choose original width, original height, new width.
- Select Calculate ratio.
- Review the main result, supporting details, and calculation method.
- Copy the result or download generated files when that option is available.
What this tool does
Simplify a width-to-height ratio and calculate a proportional dimension without stretching the image or video. The calculator divides both original dimensions by their greatest common divisor, then applies the same scale factor to the target size.
Calculation method
- Reduce the original width and height to their smallest whole-number ratio.
- Divide the target width by the original width to find the scale factor.
- Multiply the original height by that scale factor to calculate the matching height.
Example: resize 1920 × 1080 to 1280px wide
Input: Original: 1920 × 1080; New width: 1280
Result: Ratio: 16:9; New size: 1280 × 720
The width scale is 1280 ÷ 1920 = 2/3. Applying 2/3 to 1080 gives a proportional height of 720.
Practical uses
- Video thumbnails
- Responsive images
- Presentation slides
- Print and screen mockups
Accuracy tips and common mistakes
- Use the actual pixel dimensions, not the file size in KB or MB.
- Rounding to a whole pixel can create a tiny ratio difference in unusual dimensions.
- Cropping changes composition; proportional resizing does not.