Aspect ratio calculator
Enter your dimensions to get the simplified ratio, then type either a new width or a new height to get the other one without squashing anything.
Ratios, reduced
The simplified ratio comes from dividing both numbers by their greatest common divisor, which is why 1920×1080 reduces to 16:9 and 1280×1024 reduces to the less familiar 5:4. Two images with the same ratio scale into each other perfectly regardless of pixel count — the ratio is the shape, resolution is just how finely it's drawn.
Fill in either new dimension and the calculator returns its partner. That's the entire job when preparing artwork for a platform with a fixed slot: a YouTube thumbnail at 1280×720 and a stream overlay at 1920×1080 are the same 16:9 shape, so one crops into the other cleanly, while an Instagram square at 1:1 does not and will crop something out.
If your result lands on an awkward fraction of a pixel, round to a whole number and accept a fractional difference in shape — it's invisible. What isn't invisible is forcing an image into the wrong ratio, which stretches faces and is immediately obvious to anyone looking.
Questions
Why does my ratio come out as something odd like 683:384?
Because the dimensions don't share a clean divisor — usually the result of an earlier resize that rounded. Check the decimal ratio instead: if it's near 1.777 you're effectively 16:9.
How do I keep quality when resizing up?
You can't add detail that isn't there. Scaling up past roughly 200% gets soft no matter what tool you use — export from the original source at the size you need instead.
What's the difference between aspect ratio and resolution?
Ratio is the shape, resolution is the pixel count. 1280×720 and 1920×1080 are both 16:9; one simply has more pixels describing the same rectangle.