Aspect Ratio Calculator
Resize width and height while keeping the same proportions.
Your proportional size appears here
Enter the original width and height, then a new width or height. The matching dimension and simplified ratio update live — right here in your browser, with nothing sent to a server.
Runs entirely in your browserKeep proportions, locally
This calculator solves the everyday scaling problem: you have something sized W×H and you want to change one dimension without distorting it. Enter the original width and height to fix the ratio, then type a new width or a new height. The tool fills in the other value so the proportions stay identical, and shows the simplified ratio (like 16:9). Everything runs in your browser and nothing you enter is uploaded.
Common questions
How does it keep the proportions?
It fixes the ratio from your original width and height, then scales the dimension you change by the same factor. New height = new width × (original height ÷ original width), and vice versa.
What is the simplified ratio for?
It expresses the proportions as small whole numbers using the greatest common divisor — for example 1920×1080 simplifies to 16:9. It is handy for matching standard screen and video formats.
Should I enter a new width or a new height?
Either one. Fill the original width and height plus exactly one new dimension, and the calculator computes the matching value. If you fill both new fields, it uses the new width.
Does this resize an actual image file?
No — this tool only computes dimensions. To resize an image file itself, use the Image Resizer tool, which redraws the picture at your chosen size, also entirely in your browser.
Is my data sent anywhere?
No. The math runs entirely in your browser with JavaScript. Nothing you type is uploaded or stored on a server — the calculation is fully client-side and private.