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Field guide

What is aspect ratio and why does it matter?

Aspect ratio is the proportional relationship between the width and height of an image, video, or screen. It is expressed as two numbers separated by a colon, such as 16:9 or 4:3, and tells you how many units wide something is for every unit tall. A 16:9 display is 16 units wide for every 9 units tall, which is why it looks rectangular and wide.

Getting aspect ratio right is critical for anyone working with digital content. Upload a 4:3 video to a 16:9 platform and you get black bars. Crop a portrait photo to landscape without maintaining the correct ratio and subjects get stretched or cut off. Understanding aspect ratio is a fundamental skill for photographers, video editors, web designers, and social media managers.

How to calculate a simplified aspect ratio

The simplified aspect ratio is found using the Greatest Common Divisor (GCD). The GCD is the largest number that divides evenly into both the width and height. Divide both by the GCD and you have the simplest form of the ratio.

This works for any pair of dimensions. A 2560x1600 MacBook screen simplifies to 8:5, also written as 16:10. A 3000x2000 photo simplifies to 3:2, the classic DSLR camera format.

How to scale dimensions proportionally

Once you know the aspect ratio (expressed as a decimal fraction width/height), scaling is simple multiplication:

Example: You have a 1920x1080 image and want a version that is 1280 pixels wide. The height should be:

So 1280x720 is the correctly proportional scaled version of 1920x1080, and it is still 16:9.

Common aspect ratios explained

16:9 (1.78:1) - the universal widescreen

The dominant aspect ratio for digital video. Used by YouTube, Netflix, broadcast television, most computer monitors, and all major gaming consoles. Standard resolutions: 1280x720 (HD), 1920x1080 (Full HD), 2560x1440 (QHD), 3840x2160 (4K UHD). The 16:9 format was officially standardised by the SMPTE and ITU in the 1990s as a compromise between the older 4:3 television format and the wider cinema formats.

9:16 (0.56:1) - vertical video

The inverse of 16:9, designed for mobile screens held vertically. Used by TikTok, Instagram Reels, YouTube Shorts, and Snapchat Stories. Standard resolution: 1080x1920. Creating content in 9:16 from the start is always better than cropping horizontal footage, as the result is usually awkward and loses important parts of the frame.

1:1 - the square

Equal width and height. Popularised by Instagram when it launched as a square-only platform. Still the most common format for Instagram feed posts (1080x1080) and product photography on e-commerce sites. Square photos also perform well as thumbnails because they display proportionally in both grid and single-post views.

4:3 (1.33:1) - classic standard

The standard for analogue television (NTSC and PAL) and early computer monitors. Still used by many tablets and some projectors. Resolutions: 640x480 (VGA), 800x600 (SVGA), 1024x768 (XGA). Video content shot in 4:3 shows as letterboxed or pillarboxed on modern 16:9 displays.

21:9 (2.33:1) - ultrawide cinema

Used in cinematic filmmaking and ultrawide computer monitors. The format creates the wide, immersive look associated with Hollywood blockbusters. Monitors with 2560x1080 or 3440x1440 resolution use this ratio. Gaming in 21:9 provides a significantly wider field of view in supported titles.

3:2 (1.5:1) - DSLR photography

The native aspect ratio of 35mm film and most DSLR and mirrorless cameras. This ratio has been standard in photography since the Leica camera popularised 35mm film in the 1920s. Common sizes: 3000x2000, 4500x3000, 6000x4000. Printing to standard photo sizes (4x6 inches) preserves the 3:2 ratio exactly.

Aspect ratio and social media: a platform guide

Disclaimer

Aspect ratio calculations are mathematical and produce exact results. Platform dimension requirements occasionally change. Always check the official documentation for your target platform before final export.