Aspect Ratio Calculator

What is an aspect ratio?

An aspect ratio is the proportional relationship between an image’s width and height, written as two numbers separated by a colon. A 1920 × 1080 video and a 1280 × 720 video are different sizes but share the same 16:9 shape. Getting the ratio right matters whenever content has to fit a frame: video exports, social media posts, photo prints, website banners, presentation slides and screen designs. The wrong ratio means black bars, awkward crops or stretched, distorted images.

How to use the calculator

1. Enter a width and height in the first section to get the simplified ratio, its decimal form and a visual preview.
2. In the second section, choose a ratio — type it, tap a common preset, or reuse the one you just calculated.
3. Enter the new width, and the matching height appears (or enter the height to get the width).
4. Use the table at the bottom as a quick reference for common ratios and sizes.

How the ratio is calculated

The calculator divides the width and height by their greatest common divisor, the largest number that divides both evenly. For 1920 × 1080 the GCD is 120, giving 16:9. For 3000 × 2000 it’s 1000, giving 3:2. Some sizes don’t simplify neatly: 1366 × 768 becomes 683:384, which is almost exactly 16:9. In those cases the calculator also shows the closest common ratio, and the decimal form (width ÷ height) — 1.78:1 for 16:9 — makes different ratios easy to compare.

To resize while keeping the shape, multiply one side by the ratio: new height = new width × ratio height ÷ ratio width. A 16:9 frame that’s 1280 pixels wide is 1280 × 9 ÷ 16 = 720 pixels high. Where a result isn’t a whole number, the calculator also shows it rounded to whole pixels.

Common aspect ratios and where they’re used

• 16:9 — HD and 4K video, YouTube, TVs and most laptop screens.
• 9:16 — vertical video for Reels, TikTok, YouTube Shorts and Stories.
• 1:1 — square social posts and profile pictures.
• 4:5 — portrait feed posts, which take up more screen space than squares.
• 3:2 — most DSLR and mirrorless camera photos, and 4 × 6 inch prints.
• 4:3 — older TVs, iPads, many presentations and compact cameras.
• 21:9 — ultrawide monitors and a cinematic widescreen look.

Tips for working with ratios

• Crop to the target ratio before resizing, so nothing gets stretched.
• For video, pick even pixel dimensions — many encoders require them.
• In CSS, use the aspect-ratio property (for example aspect-ratio: 16 / 9) to reserve space for images and videos.

Printing an image? The Print Size & DPI Calculator tells you how large it can go. Exporting video? Estimate file sizes with the Video Bitrate Calculator, and grab brand colors from a frame with the image palette tool.