Aspect Ratio Calculator
Scale any image, video, or screen dimensions while keeping proportions perfect.
What is it?
An **aspect ratio calculator** is a tool that helps you maintain the correct proportional relationship between the width and height of an image, video frame, screen, or any rectangular element. The aspect ratio is expressed as two numbers separated by a colon — for example, 16:9 or 4:3 — and describes how wide an element is relative to its height. Aspect ratios matter everywhere in digital and print media. A YouTube video uses the 16:9 widescreen ratio. An Instagram square post uses 1:1. A traditional TV screen used 4:3. A cinema screen might use 2.39:1. When you need to resize any of these without distorting the content — stretching faces, squashing logos, or cropping key information — you need to scale proportionally, and that is exactly what this calculator does. This free online tool handles two common tasks: given a known ratio and one dimension, it calculates the missing dimension; and given any two dimensions, it simplifies them into their lowest-terms aspect ratio. It also includes a reference table of the most commonly used ratios across video, photography, social media, and print.
How to use it
- To scale dimensions: enter the original width and height, then enter either a new width or new height. The calculator fills in the missing value automatically.
- To find a ratio: enter width and height in the "Find ratio" section and get the simplified ratio instantly.
- To scale by ratio: enter a known ratio (e.g. 16:9) and one dimension to get the other.
- Use the "Common ratios" table to quickly find the dimensions you need for standard formats.
- All results update instantly as you type — no button press needed.
Why use this tool
Designers, developers, video editors, and photographers all encounter aspect ratio problems daily. Getting them wrong means images look stretched or squashed, videos show black bars, or print materials do not fit their intended format. This calculator eliminates the manual algebra and potential errors. The tool is particularly useful when working with responsive web design, where you need to convert fixed-pixel dimensions to percentage-based ones while preserving the visual proportions. It is equally valuable when preparing social media assets, converting a horizontal video to a vertical format for Reels or TikTok, or scaling product images for e-commerce listings. Everything happens in your browser — there is nothing to download and no account to create. Just enter numbers and get answers instantly.
Frequently asked questions
What is the aspect ratio of a standard HD video?
Standard HD (720p) and Full HD (1080p) video both use a 16:9 aspect ratio, meaning the width is 16 units for every 9 units of height. This is also the default ratio for most modern monitors, laptops, and smartphones in landscape mode.
What does "letterboxing" mean and how does it relate to aspect ratio?
Letterboxing refers to the black bars that appear at the top and bottom of a video when content filmed in a wider ratio (like 2.39:1 cinema) is displayed on a screen with a narrower ratio (like 16:9). The bars fill the empty space to preserve the original proportions without cropping.
How do I convert a 16:9 video to a 9:16 vertical format?
A 16:9 video is landscape orientation; 9:16 is portrait. To convert without distortion, you typically crop the sides of the horizontal video rather than stretching it. Enter your original dimensions and the new height in the calculator to find the cropped width.
What aspect ratio should I use for Instagram?
Instagram supports several ratios: 1:1 (square), 4:5 (portrait, recommended for feed posts), 16:9 (landscape), and 9:16 (Stories and Reels). The 4:5 portrait ratio maximises screen real estate in the feed.
What is the difference between pixel dimensions and aspect ratio?
Pixel dimensions (e.g. 1920×1080) are the absolute size of an image. Aspect ratio (e.g. 16:9) is the proportional relationship between width and height. Two images with different pixel counts can share the same aspect ratio — 1280×720 and 1920×1080 are both 16:9.