Aspect Ratio Calculator
Find a simplified ratio from dimensions, or calculate a missing dimension from a known ratio.
Find the Ratio
Find a Missing Dimension
How to Use the Aspect Ratio Calculator
- Enter a width and height to find the simplified ratio.
- Or enter a ratio and a known width or height to find the matching missing dimension.
Frequently Asked Questions
How is the simplified ratio calculated?
The width and height are both divided by their greatest common divisor (GCD), which reduces them to the smallest whole numbers that keep the same proportion — for example, 1920×1080 reduces to 16:9.
Why would I need to calculate a missing dimension from a ratio?
This comes up constantly when resizing images or video — if you know you need a 16:9 video that's 1280 pixels wide, you need the height to come out to exactly 720 pixels to avoid stretching or distorting the image.
Does this work for any ratio, not just common video sizes?
Yes — enter any width and height ratio, standard (like 4:3 or 16:9) or completely custom, and the missing-dimension calculator will scale to it.
Is the data I enter sent anywhere?
No — all the math happens entirely in your browser using JavaScript, so nothing you enter is ever sent to a server.