📺Aspect Ratio Calculator

This aspect ratio calculator handles three common tasks: finding the simplified aspect ratio from a set of pixel dimensions, calculating the correct height for a given width and ratio, and resizing images while preserving the original proportions. Whether you are preparing video content for a specific platform, configuring responsive design breakpoints, or scaling images for print, a screen aspect ratio calculator removes the guesswork and prevents the distortion that comes from changing width and height independently. Enter your dimensions once and get the simplified ratio, total pixel count, megapixels, and scaled dimensions in a single step.

How to Calculate Aspect Ratio from Width and Height

The aspect ratio of any rectangle is found by dividing both the width and height by their greatest common divisor (GCD), which reduces the numbers to their simplest whole-number form. For a 1920 by 1080 pixel image, the GCD of 1920 and 1080 is 120. Dividing both values by 120 gives 16 and 9, producing the familiar 16:9 ratio. A 1280 by 720 image yields the same result, because the GCD of those numbers is also the correct divisor to reach 16:9.

This is why aspect ratio is described as scale-independent. A 3840 by 2160 image and a 640 by 360 image both share the same 16:9 ratio because they encode the same proportional relationship between width and height, just at different resolutions. When you scale any image maintaining its aspect ratio, you multiply or divide both dimensions by the same factor, keeping the ratio constant.

16:9 Aspect Ratio Calculator for Video

The 16:9 widescreen ratio is the dominant standard for modern video production, streaming platforms, television, and most desktop monitors. All major HD and 4K resolutions use this ratio: 1280 by 720 (HD Ready), 1920 by 1080 (Full HD 1080p), 2560 by 1440 (2K QHD), and 3840 by 2160 (4K UHD). If you are producing video content and need to know what height corresponds to a specific width within the 16:9 ratio, select the ratio-to-dimensions mode, enter your target width, and the calculator returns the correct height automatically.

Other common ratios each have their own established uses. The 4:3 ratio was the standard for analog television and remains common on many iPad models. The 1:1 square ratio is used for Instagram feed posts and profile images across most platforms. The 21:9 ultrawide ratio appears on premium monitors and in theatrical film presentations. The 9:16 portrait ratio, which is simply 16:9 rotated vertically, is the standard for Instagram Stories, TikTok, YouTube Shorts, and all mobile-first vertical video.

Image Resize Aspect Ratio Calculator

Resizing an image without distortion requires applying the same scale factor to both dimensions. If you reduce the width of a 1920 by 1080 image to 1280 pixels, the new height must be 1080 multiplied by the ratio of 1280 to 1920, which equals 720 pixels. Changing width without recalculating height stretches the image horizontally, and changing height independently squashes it vertically. The resize mode in this calculator takes your original width and height plus a new target width and computes the correct proportional height alongside the scale factor applied.

This is especially useful when working in CSS, HTML, video encoding software, or any environment where you specify pixel dimensions manually rather than using a drag-and-drop resize tool with a built-in lock ratio option. Portrait and landscape orientations follow the same principle: the ratio simply has the larger number in the height position instead of the width position for portrait formats.

Common Aspect Ratios and Platform Requirements

Social media platforms and streaming services each specify preferred image and video dimensions. Using the correct resolution and ratio prevents automatic cropping, letterboxing, and compression artifacts. The following reference covers the most widely used platform requirements.

• YouTube standard video: 16:9 at 1920 by 1080 (Full HD) or 3840 by 2160 (4K)
• YouTube Shorts: 9:16 at 1080 by 1920
• Instagram feed square post: 1:1 at 1080 by 1080
• Instagram feed landscape: approximately 1.91:1 at 1080 by 566
• Instagram feed portrait: 4:5 at 1080 by 1350
• Instagram and Facebook Stories: 9:16 at 1080 by 1920
• Facebook post image: 1.91:1 at 1200 by 630
• Twitter/X post image: 16:9 at 1200 by 675
• DSLR camera native ratio: 3:2 (matching 35mm film standard, common print sizes such as 4 by 6 inches)

Resolution, Megapixels, and Print Size

Megapixels measure the total pixel count of an image, calculated by multiplying width by height and dividing by one million. A 1920 by 1080 image contains 2,073,600 pixels, approximately 2.07 megapixels. A 3840 by 2160 image contains 8,294,400 pixels, or 8.29 megapixels. Higher megapixel counts allow larger prints without visible pixelation, with the common guideline of 300 pixels per inch (PPI) for print quality. A 12-megapixel photo can produce a sharp 8 by 10 inch print, while a 24-megapixel image supports sharp output at 11 by 14 inches and larger.