Aspect Ratio Calculator
Find the aspect ratio of any size, then resize width or height while the proportions stay locked.
How to use the Aspect Ratio Calculator
- Enter the original width and height to see the ratio (like 16:9).
- Type a new width or height — the other value fills in to match.
- Or pick a preset ratio such as 16:9, 4:3 or 1:1 to start from.
About the Aspect Ratio Calculator
An aspect ratio is the relationship between width and height, written as two numbers such as 16:9. Type an original width and height and this tool reduces them to their simplest form using the greatest common divisor, so 1920x1080 becomes 16:9 and 1280x1024 becomes 5:4. It also shows the ratio as a single decimal, which is useful when a spec sheet quotes 1.78 rather than 16:9.
The second half works like a resizer for numbers. Tick keep the same aspect ratio, type a new width or a new height, and the other dimension is worked out proportionally and filled in for you, rounded to two decimal places. Preset buttons cover the ratios you meet most often: 16:9, 4:3, 21:9, 1:1, 9:16 and 3:2, so you can jump straight to widescreen video, classic photos, ultrawide monitors, squares, vertical phone video or 35mm-style stills.
Two honest limits are worth stating. It works only from the numbers you type: it does not open an image file or read its real pixel dimensions, so to scale an actual photo use the image resizer. And because the computed side is rounded to two decimals, it can land on a fraction of a pixel, so round to a whole number before you export, since screens cannot show half a pixel.
Frequently asked questions
What is an aspect ratio?
It is the proportion between width and height, written as two numbers separated by a colon, like 16:9. It describes shape, not size: a 16:9 image has the same proportions whether it is 1920x1080 or 3840x2160. This tool reduces any width and height you enter to that simplest form.
How does it turn 1920x1080 into 16:9?
It finds the greatest common divisor of the two numbers and divides both by it. For 1920 and 1080 the greatest common divisor is 120, and 1920 divided by 120 is 16 while 1080 divided by 120 is 9, giving 16:9. The same method simplifies any pair of dimensions you type.
Can it read the dimensions of my image file?
No. It works only from the width and height you type in, not from an uploaded file. To scale an actual photo and keep its proportions, use the image resizer, which reads the file's real pixel size for you.
Why is the calculated dimension not a whole number?
The proportional result is rounded to two decimal places, so it can come out as a fraction of a pixel, such as 853.33. Screens display whole pixels only, so round to the nearest whole number before exporting your file.
What do the preset ratio buttons do?
Each button loads a common ratio for you: 16:9 for widescreen video, 4:3 for older photos and screens, 21:9 for ultrawide monitors, 1:1 for squares, 9:16 for vertical phone video and 3:2 for many stills cameras. Pick one instead of typing the numbers by hand.