Aspect Ratio Calculator
Keep proportions right when resizing.
Aspect Ratio Calculator finds the missing dimension when you resize something proportionally, reduces any width and height to its simplest ratio, and lists common ratios like 16:9, 4:3, 21:9 and 1:1 with their pixel dimensions. Useful for video, images and CSS layout work. The maths runs in the page.
Loading Aspect Ratio Calculator…
Runs entirely on your device. No file or text you enter here is uploaded. How to verify it.
How to use Aspect Ratio Calculator
- Enter the original width and height.
- Type the new width or the new height.
- Read the missing value and the simplified ratio.
Questions about Aspect Ratio Calculator
How is the ratio simplified?
By dividing both numbers by their greatest common divisor. 1920×1080 reduces to 16:9; 1366×768 reduces to 683:384, which is why that old laptop resolution is not quite 16:9 and letterboxes slightly.
What ratio should I use for video?
16:9 for standard landscape video, 9:16 for vertical social video, 1:1 for feed posts, and 21:9 for cinematic widescreen. All are one click away with their standard pixel dimensions.
Can I get non-integer results?
They are shown, but rounded to whole pixels for the practical answer, with a note when the rounding shifts the ratio by more than a hair.
What is the difference between aspect ratio and resolution?
Resolution is the pixel count, the ratio is the shape. 1920×1080 and 1280×720 are different resolutions with the same 16:9 shape, so neither one letterboxes against the other. This tool answers the shape question — it does not resize a file.
Does it change my image, or only tell me the numbers?
Only the numbers. It works out the dimensions and the scale factor; the actual resizing is a separate job, and the image resizer listed below does it in your browser without uploading the file.
Is Aspect Ratio Calculator really free, with no limits?
Yes. There is no account, no daily cap, no file-size tier and no watermark, because there is no server cost to recover. The site is funded by clearly disclosed partner recommendations on the Partners page, never by metering the tools.
Are my files or text uploaded when I use Aspect Ratio Calculator?
No. Everything is processed by JavaScript running in your browser, on your device. You can verify it: open your browser's developer tools, switch to the Network tab, and use the tool. You will see no request carrying your data — because there is nowhere for it to go.