Aspect Ratio Calculator
Simplify a width × height to its aspect ratio, then resize while keeping that ratio.
Edit a width or height — the other side is recalculated to keep the ratio.
Find the aspect ratio of any size and resize it cleanly
Enter the original width and height of a screen, video, or image and this calculator reduces it to its simplest aspect ratio — for example 1920×1080 becomes 16:9 and 3840×2160 also becomes 16:9. It uses the greatest common divisor so the ratio is always in lowest terms, and everything is computed live in your browser with no uploads.
The resize row keeps that ratio for you. Type a new width and the matching height appears automatically; type a new height instead and the width is filled in. This is the fast way to scale a design, embed, or thumbnail to a different size without stretching or letterboxing. The preset buttons (16:9, 4:3, 21:9, 1:1, 3:2, 9:16) load the most common screen and video ratios so you can resize against a standard instantly.
FAQ
What does an aspect ratio like 16:9 mean? It is the proportion of width to height. 16:9 means for every 16 units of width there are 9 units of height, regardless of the actual pixel count.
How is the ratio simplified? The width and height are divided by their greatest common divisor (GCD). For 1920×1080 the GCD is 120, giving 16:9.
Why does resizing sometimes produce a fractional pixel? Keeping a ratio exactly can yield a non-integer dimension (e.g. 1000px wide at 16:9 is 562.5px tall). Round to the nearest whole pixel for real assets; the tool shows the exact value.
Is my data sent anywhere? No. The calculation is pure math that runs entirely in your browser — nothing is uploaded.