Aspect Ratio Calculator

What is an aspect ratio?

An aspect ratio is the proportional relationship between an image's width and height, written as width:height. You reduce it the same way you simplify a fraction — divide both numbers by their greatest common divisor. A 1920×1080 image becomes 16:9 because 1920 and 1080 share a common factor of 120. The key property is that the ratio is independent of size: a tiny thumbnail and a 4K poster can share exactly the same 16:9 shape. That's why ratios are the right unit when you care about how something looks rather than how many pixels it contains.

Common aspect ratios and where they're used

16:9 is the universal widescreen standard — TVs, laptop and desktop monitors, YouTube, and most streaming video. 4:3 is the older, squarer format from CRT displays and early digital cameras, still seen on some tablets and projector slides. 3:2 dominates stills photography (most DSLR and mirrorless sensors). 1:1 square is the Instagram-grid classic, and 9:16 vertical is the format for phone-first video: Reels, TikTok, Shorts, and Stories. At the wide end, 21:9 and 32:9 ultrawide ratios power cinematic film and multi-window productivity monitors. Choosing the right ratio up front saves you from letterboxing, cropping, or awkward bars later.

How to resize while keeping the ratio

The most common resize mistake is changing only one dimension — set a new width but leave the old height and your content stretches or squashes. To resize proportionally, hold the ratio constant: new height = new width × (ratio height ÷ ratio width). For a 16:9 image scaled to 1280 wide, the height is 1280 × (9 ÷ 16) = 720. This calculator does that for you: click Lock Ratio or pick a preset, then type either dimension and the other updates automatically so the shape never changes. When you need exact output for an export or an upload with strict pixel limits, switch back to entering raw pixel values and read off the simplified ratio to confirm you haven't distorted anything.