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About Aspect Ratio Calculator Online
This tool computes width, height, or aspect ratio given two of the three values. Enter any two and the third is calculated. It also recognises common named ratios (16:9, 4:3, 21:9, 1:1, 9:16) and converts them to width-and-height pairs at any target dimension.
Aspect ratio matters whenever images, videos, or screens must be presented at a different size without distortion. Resizing a 1920×1080 frame to 800px wide should produce 800×450 — anything else stretches or crops the original.
Use it for web layout (responsive images), photo editing (target export size), video production (matching social platform formats), and screen sizing (TVs, monitors, projectors).
How to use this tool
How to compute the missing dimension at a target aspect ratio
Source dimensions
"Original width" and "Original height" are the source size in pixels (or any unit, as long as both match). Use them to define the ratio that must be preserved.
Target width
"Target width" is the new width you want to fit. The tool will scale height proportionally. To target a height instead, swap width and height in all three fields — the math is symmetric.
Press Run
Result returns targetHeight = Math.round(targetWidth × originalHeight / originalWidth). Result is rounded to the nearest integer pixel; sub-pixel precision isn't preserved.
Common ratio examples
16:9 → from 1920×1080, target 1280 gives height 720. 4:3 → from 800×600, target 1024 gives 768. 1:1 → width and height are always equal.