Aspect Ratio Calculator
Preserve an image or video proportion by calculating the matching height for a new width and simplifying the original ratio.
Calculate a missing image dimension
How this tool works
An aspect ratio describes the proportional relationship between width and height. This calculator scales height from a requested width and also reduces whole-number source dimensions to a familiar ratio where possible.
New height equals new width multiplied by original height divided by original width. The reduced ratio divides both rounded source dimensions by their greatest common divisor.
How to use it
- Enter the original width and height.
- Enter the desired new width in the same unit.
- Use the calculated height to resize without changing proportions.
Worked examples
Full HD resize
- Input
- 1920×1080 resized to 1280 pixels wide
- Output
- 720 pixels high
The new width is two thirds of the original width, so the height is also multiplied by two thirds, preserving the 16:9 relationship.
Square artwork
- Input
- 1000×1000 resized to 600 pixels wide
- Output
- 600 pixels high
A square has a 1:1 relationship. Matching width and height at every scale preserves the original shape without stretching.
Limitations
- Rounding to whole pixels can introduce a very small proportional difference.
- The tool calculates dimensions but does not resize or crop the image file.