Aspect ratio calculator

An aspect ratio describes the proportional relationship between width and height, written as width:height. Designers, video editors and developers use it to resize images without distortion, choose video export settings and build responsive layouts. This calculator does two things: it reduces any dimensions to the simplest ratio, and it solves a missing dimension when you know the ratio and one side.

How to use it

1. To find a ratio, enter a width and height, for example 1920 and 1080.
2. To resize, enter the ratio and one known side; the other side is calculated.
3. Copy the result for your editor, CSS or export settings.

How the math works

The ratio is simplified by dividing both sides by their greatest common divisor. For 1920 × 1080 the GCD is 120, so the ratio is 16:9. To find a missing height for a new width, use height = width × (ratio height / ratio width): a 1280 px wide 16:9 video needs a height of 1280 × 9 / 16 = 720 px.

Common aspect ratios

• 16:9: HD and 4K video, most monitors and YouTube.
• 4:3: older TVs, many tablets and presentation slides.
• 1:1: square social media posts.
• 9:16: vertical video for Reels, Shorts and TikTok.
• 21:9: ultrawide monitors and cinematic video.
• 3:2: DSLR photos and many laptops.

In CSS

Modern browsers support the aspect-ratio property, for example aspect-ratio: 16 / 9;, which keeps an element's proportions while its width changes.