Aspect Ratio Calculator

About the Aspect Ratio Calculator

The aspect ratio of an image, video or screen is the relationship between its width and its height. It decides whether a video fills a TV or leaves black bars, whether a photo fits a frame or needs cropping, and whether an image appears correctly in a social media feed. When resizing, keeping the same aspect ratio is what stops pictures from looking stretched or squashed.

This aspect ratio calculator works in two ways. Find the ratio of any width and height — 1920 × 1080 is 16:9 — with the decimal ratio, pixel count and the nearest common ratio. Or resize to a new width or height while keeping the same ratio: 16:9 at 1280 wide is 1280 × 720.

How to Use the Aspect Ratio Calculator

To find a ratio, choose find the ratio and enter the width and height in pixels.

To resize, choose resize to the same ratio, enter the ratio (such as 16 and 9), and fill in either the new width or the new height.

How the Aspect Ratio Is Worked Out

  greatest common divisor (gcd) of width and height
  ratio        =  width ÷ gcd  :  height ÷ gcd
  decimal      =  width ÷ height  :  1
  new height   =  new width × ratio height ÷ ratio width
  new width    =  new height × ratio width ÷ ratio height

Step-by-Step Example

1920 × 1080.

  gcd(1920, 1080)       =  120
  1920 ÷ 120 : 1080 ÷ 120  =  16:9
  Decimal:  1920 ÷ 1080  =  1.778:1

Resize 16:9 to 1280 wide.

  Height:   1280 × 9 ÷ 16  =  720   →  1280 × 720

Common Aspect Ratios

Resolutions and Ratios

Many screen resolutions share a ratio: 1280 × 720, 1920 × 1080, 2560 × 1440 and 3840 × 2160 are all 16:9. Some familiar sizes are not exact: 1366 × 768 simplifies to 683:384, about 1.779:1, very close to 16:9 but rounded for hardware reasons. Ultrawide monitors marketed as 21:9 are usually 2560 × 1080 (64:27, 2.37:1) or 3440 × 1440 (43:18, 2.39:1).

Resizing Without Distortion

When you change only the width or only the height of an image, it stretches. Always scale both by the same factor, which keeps the ratio. If you need a different ratio — turning a 16:9 video into a 9:16 vertical clip, or fitting a 3:2 photo into a 4:5 frame — crop part of the picture instead of stretching it, or add borders (letterboxing or pillarboxing).

Video and Photography

Video editors set a project's aspect ratio before editing; mixing footage of different ratios creates black bars. Photographers choose the ratio of a print or frame, then crop: a 3:2 photo printed at 10 × 8 inches (5:4) loses part of its longer side. Social platforms display different ratios in feeds, profiles and stories, so it is worth checking the current recommended sizes before exporting.

Aspect Ratio in Web Design

On the web, images and videos are often placed in containers that change size with the screen. Reserving space with the right aspect ratio stops the page from jumping as images load, which improves both the reading experience and search engine measures of page stability. CSS has an aspect-ratio property for exactly this: setting aspect-ratio: 16 / 9 on a video container keeps it the right shape at any width. For responsive images, supplying width and height attributes lets the browser work out the ratio before the image arrives.

Printing Photos

Standard print sizes do not all share the same ratio. A 6 × 4 inch print is 3:2, matching most camera sensors exactly. A 7 × 5 print is 1.4:1, 10 × 8 is 5:4 and 12 × 8 is 3:2 again. When a photo's ratio differs from the print's, the lab either crops the picture or adds white borders, so check the preview and choose where to crop before ordering. For a 4:3 phone photo, 8 × 6 and 12 × 9 prints avoid cropping.

Pixels, Megapixels and Ratio

The same ratio can come at very different sizes. A 16:9 image might be 640 × 360 pixels, a quarter of a megapixel, or 7680 × 4320, over 33 megapixels. The ratio says nothing about quality; the pixel count and the display size decide how sharp the image looks.

Phones and Tall Screens

Modern phones have tall screens, often around 19.5:9 or 20:9, so a 16:9 video fills the width in landscape but leaves small bars at the sides. Vertical 9:16 video fills most of the screen when the phone is held upright, which is why short-form video platforms and phone-first apps use it for almost everything they show on the main feed.

Understanding Your Result

Aspect ratio gives the simplified ratio, or the new size when resizing.

Ratio gives the decimal ratio and the orientation.

Size gives the pixel count, or the size rounded to whole pixels.

Common ratio names the nearest standard ratio.

Worth knowing lists typical ratios for screens, photos and social media.

When Should You Use This Calculator?

Resizing images for websites.

Exporting video for different platforms.

Choosing a monitor or TV.

Cropping photos for prints and frames.

Designing layouts that scale on any screen.

Common Mistakes

Changing only one dimension and stretching the image.

Assuming every widescreen is exactly 16:9.

Forgetting to crop when changing ratio.

Mixing portrait and landscape values.

Rounding sizes so they no longer match the ratio.