Aspect Ratio Calculator
Aspect Ratio Calculator is a free image tool that runs directly in your browser with no account required.
About this tool
When you scale an image or video frame, changing the width without recalculating the height stretches or squashes the picture. This calculator takes your original dimensions and a new width, then returns the matching height so the proportions stay identical. It works for any pixel dimensions, from thumbnails to 4K frames.
How to use
- Enter the current dimensions in Original width and Original height.
- Type the target width in New width.
- Read the New height value, which is rounded to the nearest whole pixel.
- Check the Ratio field to confirm the original proportion being preserved.
Frequently asked questions
What formula does the calculator use?
New height equals new width multiplied by original height divided by original width. The result is rounded to the nearest whole pixel because screens cannot display fractional pixels.
Can I calculate a new height instead of a new width?
The form takes a new width and returns the height. If you know the height you want, swap your numbers: enter the original height as Original width and the original width as Original height, then put your target height in New width.
Why does the Ratio field show 1920:1080 instead of 16:9?
The tool displays the ratio using the exact dimensions you entered rather than reducing it to the smallest equivalent form. 1920:1080 and 16:9 describe the same proportion.
Does this tool resize my actual image file?
No, it only calculates dimensions. To resize a real file, use the Image Resizer on this site, which processes the image in your browser.
What happens if I enter zero or a negative number?
The calculator asks for positive dimensions and will not produce a result until width, height, and new width are all greater than zero.