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Aspect Ratio & Dimensions Calculator

Calculate image dimensions, resize content for social media (16:9, 9:16, 4:5), and find missing width or height.

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Mastering Aspect Ratios: The Ultimate Guide for Designers & Editors

In the digital world, one size rarely fits all. Whether you are a video editor ensuring your 4K footage fits on a smartphone screen, or a social media manager resizing a banner for a LinkedIn header, understanding Aspect Ratio is critical. Our Aspect Ratio & Dimensions Calculator solves the most common problem in digital design: 'If I change the width to 1080px, what should the height be?'

What is Aspect Ratio?

An aspect ratio describes the proportional relationship between an image's width and its height. It is commonly written as two numbers separated by a colon, like 16:9. It's important to note that aspect ratio represents the relationship, not the actual resolution. A 1920x1080 video and a 3840x2160 (4K) video both have the same 16:9 aspect ratio.

Common Social Media Ratios Cheat Sheet (2025)

Using the wrong ratio often results in your content being cropped awkwardly or having ugly black bars (letterboxing) added to the sides. Use this guide with our calculator to get perfect dimensions every time.

  • 16:9 (Widescreen): The standard for YouTube videos, TV broadcasts, and most computer monitors. Common resolutions: 1920x1080 (HD), 3840x2160 (4K).
  • 9:16 (Vertical Video): The king of mobile content. Essential for TikTok, Instagram Reels, and YouTube Shorts. Common resolution: 1080x1920.
  • 4:5 (Portrait): The secret weapon for Instagram Feed Posts. It takes up more vertical screen real estate than a square, leading to higher engagement. Resolution: 1080x1350.
  • 1:1 (Square): The classic Instagram format and great for Facebook carousel ads. Resolution: 1080x1080.
  • 21:9 (Ultrawide/Cinematic): Used in feature films and ultrawide gaming monitors to provide an immersive field of view.

How to Use This Calculator

This tool features two powerful modes designed for different workflows:

1. Find Dimensions Mode (Resizing)

Use this when you know your target ratio (e.g., 16:9) and one dimension (e.g., Width = 1920), but need to find the other. This prevents image stretching and distortion.

  • Select a preset like '16:9' or enter a custom ratio.
  • Enter your known Width (or Height).
  • The tool instantly calculates the missing pixel value.

2. Find Ratio Mode (Reverse Engineering)

Use this when you have an image with weird dimensions (e.g., 800x600) and want to know what aspect ratio it is.

  • Enter the Width (800) and Height (600).
  • The tool simplifies the fraction using the Greatest Common Divisor (GCD) algorithm to tell you it is exactly 4:3.

Frequently Asked Questions

How do I calculate aspect ratio manually?

To find the aspect ratio of a resolution like 1920x1080, you divide both numbers by their Greatest Common Divisor (GCD). The GCD of 1920 and 1080 is 120.
1920 / 120 = 16
1080 / 120 = 9
Thus, the ratio is 16:9.

Why does my video have black bars?

Black bars appear when the aspect ratio of your content doesn't match the aspect ratio of the screen (or player). For example, watching a 21:9 movie on a 16:9 TV results in horizontal bars (letterboxing). To fix this, you must either crop the video (losing side content) or resize it to match the player's ratio.

Does changing aspect ratio affect quality?

Changing the ratio often involves cropping or stretching. Cropping removes pixels, preserving quality but losing content. Stretching distorts the image. Resizing proportionally (what this calculator does) maintains the original image integrity without distortion.