Aspect Ratio Calculator Online — 16:9, 4:3, 1:1 Guide

How to Use the Aspect Ratio Calculator

1. Open the Aspect Ratio Calculator.
2. Click a preset (16:9, 4:3, etc.) or enter a custom ratio in the W:H fields.
3. Enter the width — the height is calculated automatically.
4. Or enter the height — the width is calculated automatically.
5. The Detected ratio shows the simplified ratio for any custom dimensions you enter.
6. Click Copy to copy the result to your clipboard.

Common Aspect Ratios

Platform-Specific Aspect Ratio Requirements

YouTube

All YouTube videos should use 16:9. The minimum recommended resolution is 1280×720 (720p). For the best quality across all devices: 1920×1080 (1080p) or 3840×2160 (4K). Vertical 9:16 content is supported as YouTube Shorts, which displays differently from regular uploads.

Instagram

Instagram supports three ratios for feed posts: 1:1 (square, 1080×1080), 4:5 (portrait, 1080×1350 — maximizes vertical feed space), and 1.91:1 (landscape, 1080×566). Reels and Stories use 9:16 (1080×1920). Uploading the wrong ratio results in cropping, so calculate dimensions before exporting.

Open Graph / Social Sharing

Facebook, LinkedIn, and Twitter preview images use approximately 1.91:1 (1200×628px). Twitter card images are 2:1 (1200×600px) or 1:1 (1200×1200px) for summary cards. Using the correct ratio prevents ugly cropping when your URL is shared.

Maintaining Aspect Ratio in CSS

The aspect-ratio property (modern)

.video-container {
  width: 100%;
  aspect-ratio: 16 / 9;
  background: #000;
}

.square-card {
  width: 300px;
  aspect-ratio: 1;
}

Supported in all modern browsers since 2021. The simplest and most readable approach.

The padding-top hack (legacy support)

.video-wrapper {
  position: relative;
  padding-top: 56.25%; /* 9/16 × 100% */
}
.video-wrapper iframe {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}

This technique works in all browsers including IE. The padding percentage is calculated as (height / width) × 100. For 4:3: 75%. For 1:1: 100%. For 21:9: 42.86%.

Common Questions

What does the "detected ratio" in the tool mean?

When you enter width and height values, the tool divides both by their greatest common divisor to find the simplest ratio. For example, 1920×1080 reduces to 16:9 (dividing both by 120). This is the canonical ratio for those dimensions.

How do I calculate the height for a 16:9 image that is 800px wide?

Height = Width × (9 ÷ 16) = 800 × 0.5625 = 450px. Or use the calculator: select the 16:9 preset, enter 800 in the width field, and the height updates to 450 automatically.

What is the aspect ratio of a full HD 1920×1080 monitor?

1920 ÷ 1080 = 1.778, which reduces to 16:9 (divide both by 120). All common HD and 4K resolutions (720p, 1080p, 1440p, 4K) are 16:9.