Aspect Ratio Calculator
Calculate a locked aspect ratio and matching dimensions for resizing images or video. Free to use, no signup required for occasional use.
Aspect ratio: 16:9
Change either new width or new height and the other locks to the original aspect ratio automatically.
What is the Aspect Ratio Calculator?
The Aspect Ratio Calculator works out the proportional relationship between an image or video's width and height, expressed as a simplified ratio like 16:9 or 4:3, and helps you calculate matching dimensions when resizing while preserving that ratio. This is useful for designers, video editors, and developers who need to resize an image or video frame without distorting it — for example, fitting a photo into a specific width while automatically getting the correct proportional height.
How to use it
Enter your original width and height to see the simplified aspect ratio calculated automatically. Then enter either a new width or a new height in the second section, and the other value updates automatically to keep the same proportions as the original.
Frequently asked questions
How is the simplified ratio calculated?
It divides both the width and height by their greatest common divisor to reduce the ratio to its simplest whole-number form.
Can I use this for video dimensions too?
Yes, the same proportional math applies whether you're resizing an image, a video frame, or any rectangular element.
What if I only know one new dimension?
Enter just the width or just the height you need, and the calculator fills in the other value to match the original ratio.