Aspect Ratio Calculator -- Image & Video Sizes

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Common Aspect Ratios

What Is an Aspect Ratio?

An aspect ratio is the proportional relationship between the width and height of an image, video, or screen. It is written as two numbers separated by a colon — for example, 16:9. This means for every 16 units of width, there are 9 units of height. The ratio stays constant regardless of the actual pixel dimensions: both 1920×1080 and 3840×2160 are 16:9.

How to Calculate Aspect Ratio

To find the aspect ratio from pixel dimensions, divide both width and height by their greatest common divisor (GCD):

Ratio = Width ÷ GCD(Width, Height) : Height ÷ GCD(Width, Height)

Step-by-Step Example

Input: 1920 × 1080

1. Find GCD of 1920 and 1080 → 120
2. Divide width: 1920 ÷ 120 = 16
3. Divide height: 1080 ÷ 120 = 9
4. Aspect ratio: 16:9

Calculating Missing Dimensions

If you know the ratio and one dimension, calculate the other:

• Find height: Height = Width × (Ratio Height ÷ Ratio Width). For 16:9 at 2560px wide: 2560 × (9 ÷ 16) = 1440.
• Find width: Width = Height × (Ratio Width ÷ Ratio Height). For 16:9 at 720px tall: 720 × (16 ÷ 9) = 1280.

Aspect Ratios for Social Media and Video Platforms

Each platform has preferred aspect ratios. Using the wrong ratio causes cropping, black bars, or reduced quality. Here is a quick reference:

Platforms may update their specifications. These values reflect common guidelines as of 2025.

When to Use Each Aspect Ratio

• 16:9 — HD widescreen: Standard for YouTube, TV broadcasts, computer monitors, and most video content. Use this for any landscape video or screen-targeted design.
• 4:3 — Classic format: Used for iPad displays, presentation slides (PowerPoint, Keynote), and legacy video. Choose this for presentations or content viewed on tablets.
• 1:1 — Square: Ideal for Instagram feed posts, profile pictures, and album art. Works well in grid layouts.
• 9:16 — Vertical video: Required for TikTok, Instagram Reels/Stories, and YouTube Shorts. Matches the natural orientation of smartphones held upright.
• 21:9 — Ultrawide: Used for ultrawide monitors and cinematic video. Provides immersive horizontal framing for films and gaming content.
• 3:2 — Photography: Standard for 35mm film and most DSLR/mirrorless cameras. Common for printed photos (4×6 inches) and some laptop displays (Microsoft Surface).
• 4:5 — Portrait: Instagram's preferred portrait format for feed posts. Taller than square, uses more vertical screen space in the feed.

Common Mistakes

• Confusing ratio with resolution: 16:9 is a ratio, not a resolution. Both 1280×720 and 3840×2160 are 16:9 — they differ in pixel count, not shape.
• Ignoring platform requirements: Uploading a 16:9 video to TikTok (which expects 9:16) results in a tiny letterboxed video or aggressive auto-cropping. Always check the platform's preferred ratio before exporting.
• Stretching instead of cropping: Forcing an image into a different ratio by stretching distorts the content. Always crop or add padding (letterboxing/pillarboxing) instead.
• Using non-standard ratios accidentally: A 1920×1000 image is not 16:9 — it is 1.92:1. Even small deviations can cause unexpected cropping on platforms that enforce strict ratios.
• Forgetting about pixel density: A 1920×1080 image looks sharp on a 1080p display but may appear blurry on a 4K screen. For high-DPI displays, export at 2× the display dimensions (e.g., 3840×2160 for a 1920×1080 viewport).
• Mixing up 21:9 and 2.39:1: Most "ultrawide" monitors are actually 64:27 (≈2.37:1), not exactly 21:9 (≈2.33:1). For cinematic content, the actual ratio depends on the film format. "21:9" is a marketing shorthand.

Frequently Asked Questions

What is an aspect ratio?

An aspect ratio is the proportional relationship between the width and height of an image, video, or screen. It is written as two numbers separated by a colon — for example, 16:9. A 16:9 ratio means for every 16 units of width, there are 9 units of height. Both 1920×1080 and 3840×2160 share the same 16:9 ratio because the proportions are identical.

What is the most common aspect ratio for video?

16:9 is the most common aspect ratio for video. It is the standard for HD (1920×1080), 4K (3840×2160), YouTube, and most modern monitors and TVs. Before widescreen adoption, 4:3 was the dominant ratio for standard-definition television.

What aspect ratio is used for TikTok and Instagram Reels?

TikTok, Instagram Reels, and YouTube Shorts use a 9:16 vertical aspect ratio. This is the inverse of 16:9 and matches the portrait orientation of smartphones. The standard resolution is 1080×1920.

How do I calculate the height from width and aspect ratio?

Divide the width by the ratio's width value, then multiply by the ratio's height value: Height = Width × (Ratio Height ÷ Ratio Width). For a 16:9 ratio at 1920px wide: 1920 × (9 ÷ 16) = 1080.

What aspect ratio is 1920×1080?

1920×1080 is 16:9. This resolution is called Full HD (1080p). To find the ratio, divide both numbers by their greatest common divisor: GCD(1920, 1080) = 120, giving 16:9.

What is the difference between 16:9 and 16:10?

16:9 is slightly wider than 16:10. At the same width, 16:10 is taller — for example, 1920×1200 vs. 1920×1080. 16:9 is standard for video and gaming. 16:10 is common on productivity laptops (MacBook, Dell XPS) because the extra vertical space benefits documents and code.

What aspect ratio should I use for social media?

It depends on the platform: Instagram feed posts use 1:1 (square) or 4:5 (portrait). Stories and Reels use 9:16. YouTube uses 16:9. Twitter/X and Facebook feed images work well at 16:9 or 1.91:1. LinkedIn link previews use 1.91:1.

What is the 4:3 aspect ratio used for?

4:3 was the standard for analog television and early computer monitors. Today it is used for iPad screens, presentation slides (PowerPoint/Keynote defaults), and some security cameras. Common 4:3 resolutions include 1024×768 and 2048×1536.

What is the 21:9 ultrawide aspect ratio?

21:9 is a label for ultrawide monitors and cinematic video. Common resolutions are 2560×1080 and 3440×1440. Most "ultrawide" monitors are actually closer to 2.37:1 (64:27), but 21:9 is the conventional shorthand. It provides a wider field of view for gaming and more horizontal workspace for productivity.

How do I find the aspect ratio of an existing image?

Check the image dimensions (right-click → Properties or Get Info), then divide both by their greatest common divisor. For 4000×3000: GCD = 1000, ratio = 4:3. For non-standard sizes, divide width by height to get the decimal ratio (e.g., 1.333 ≈ 4:3).

What are letterboxing and pillarboxing?

Letterboxing adds horizontal black bars above and below a wide video when displayed on a narrower screen (e.g., 21:9 on a 16:9 display). Pillarboxing adds vertical bars on the sides when a narrow video is shown on a wider screen (e.g., 4:3 on a 16:9 display). Both preserve the original aspect ratio without distortion.

Does this calculator store my data?

No. All calculations run entirely in your browser using JavaScript. No data is sent to any server. Your dimensions and ratio selections are never stored or tracked.

Related Tools

• Aspect Ratio Visualizer — compare multiple aspect ratios side by side with visual overlays
• Image to PDF Converter — convert images to PDF while preserving dimensions
• Screen Size Visualizer — compare screen sizes and resolutions across devices
• Viewing Distance Calculator — find the ideal viewing distance for any screen size
• Pixel Density Visualizer — visualize PPI and pixel density for different displays

Privacy & Limitations

• Client-side only. No data is sent to any server. No cookies, no tracking of dimensions entered.
• Integer rounding. Calculated dimensions are rounded to the nearest pixel. For some ratios, this introduces a sub-pixel error (e.g., 16:9 at 1366px wide gives 768.375, rounded to 768).
• Standard ratios only. This tool works with numeric ratios. Anamorphic or non-square pixel ratios (PAR) used in some broadcast formats are not accounted for.
• Resolution table is illustrative. The "Common Resolutions" list shows standard widths scaled to your chosen ratio. Your device or platform may require specific resolutions not listed.

Aspect Ratio Calculator FAQ