📐 Aspect Ratio Calculator
Pick an aspect ratio like 16:9 and type one dimension — the other is filled in so your image or video keeps its shape without stretching. Everything runs instantly, entirely on your device.
Common ratios
Aspect ratio
Pixel dimensions
Simplified ratio
16 : 9
As a decimal (W ÷ H)
1.7778
Pick a ratio (or type your own), then enter one pixel dimension — with the lock on, the other follows automatically so the image or video keeps its shape. 🔒 Runs entirely in your browser.
How the aspect ratio calculator works
For a ratio W:H, the missing dimension is found by cross-multiplication: new height = new width × H ÷ W, and new width = new height × W ÷ H. To turn a pixel size into a ratio, divide both sides by their greatest common divisor (GCD) — 1920×1080 ÷ 120 = 16:9.
Example: At 16:9, a width of 1280 px gives a height of 1280 × 9 ÷ 16 = 720 px (so 1280×720). Reducing 1920×1080 by its GCD of 120 gives the ratio 16:9.
Aspect ratio is the proportional relationship between width and height, independent of actual size — 1280×720, 1920×1080 and 3840×2160 are all 16:9. Keeping the ratio fixed while changing one dimension is what stops an image or video being squashed or stretched. Common ones: 16:9 for HD video and most screens, 9:16 for vertical Reels/TikTok/Stories, 1:1 for square social posts, 4:3 for older displays and many slides, 3:2 for most DSLR photos, and 21:9 for ultrawide/cinematic. Note that changing the ratio does not add detail — upscaling to a larger size still just enlarges the pixels you have.
Frequently asked questions
How do I calculate aspect ratio?
Divide the width by the height and reduce to the simplest whole-number ratio using the greatest common divisor. 1920×1080 has a GCD of 120, so it reduces to 16:9. This calculator does it automatically — enter the pixel size and read off the ratio.
How do I find a dimension for a given ratio?
Cross-multiply: for a W:H ratio, new height = new width × H ÷ W. At 16:9, a 1280 px width gives 1280 × 9 ÷ 16 = 720 px. Enter the ratio and one dimension and the other is filled in for you.
What is a 16:9 aspect ratio in pixels?
There is no single pixel size — 16:9 is a proportion. Common 16:9 resolutions are 1280×720 (720p), 1920×1080 (1080p) and 3840×2160 (4K UHD). All share the same shape.
Why does keeping the aspect ratio matter?
Changing width and height independently to a different ratio squashes or stretches the image, distorting faces and circles. Locking the ratio recalculates the second dimension so the content keeps its true proportions.
What aspect ratio should I use for social media?
Broadly: 1:1 (square) or 4:5 for feed posts, 9:16 (vertical) for Reels, TikTok and Stories, and 16:9 for landscape video and YouTube. Each platform has its own recommended pixel sizes within those ratios.
Does changing the aspect ratio reduce quality?
Cropping to a new ratio removes pixels but keeps sharpness; stretching to a new ratio distorts the image. Scaling to a larger size at the same ratio does not add real detail — it just enlarges the existing pixels, which looks softer.
Is this aspect ratio calculator accurate and private?
Yes. It uses the standard published formula, shows its working under every result, and computes locally in your browser — your inputs are never sent to a server, and the page works offline.