Aspect Ratio Calculator
Reduce any pixel dimension to its simplest ratio.
Reading the two numbers
The simplified ratio comes from dividing both dimensions by their greatest common divisor, so 1920×1080 reduces to 16:9. The decimal underneath it is just width divided by height, and it is the more useful of the two when a size is nearly standard rather than exactly so.
1366×768 is the case that catches people out. It is sold as a 16:9 laptop screen, but the GCD reduction gives 683:384, because 1366 is not exactly sixteen ninths of 768. The decimal shows why nobody notices: 1.779 against 16:9's 1.778. When the reduced ratio looks strange, compare the decimals before assuming something is wrong.
Scaling is the operation this feeds into. Multiply both dimensions by the same factor and the shape is preserved; change one alone and the image distorts. That is the entire content of “keep the aspect ratio”.
Frequently asked questions
How is an aspect ratio calculated?
Divide both dimensions by their greatest common divisor. For 1920×1080 the GCD is 120, giving 16:9. The decimal form is simply width ÷ height, which is 1.78 for 16:9.
Why does my resolution give an odd ratio like 683:384?
Because it is not exactly a standard ratio. 1366×768 is the classic example — it is marketed as 16:9 but reduces to 683:384, since 1366 is not exactly 16/9 of 768. The decimal figure, 1.779 against 1.778, shows how close it actually is.
What ratio should I use for social images?
Open Graph and Twitter cards expect 1200×630, which is 40:21 or roughly 1.91:1. Instagram feed posts are 1:1 or 4:5, and stories and reels are 9:16. Using the wrong one gets your image cropped rather than rejected.
How do I scale a size while keeping the ratio?
Multiply both dimensions by the same factor. To halve 1920×1080, take both to 960×540 — the ratio is unchanged at 16:9. Changing only one dimension distorts the image.
What is the difference between aspect ratio and resolution?
Resolution is the actual pixel count; aspect ratio is the shape those pixels form. 1280×720 and 1920×1080 are different resolutions with the identical 16:9 shape.