What an aspect ratio calculator does
The aspect ratio is the proportional relationship between an image or screen's width and its height, written as two numbers separated by a colon — for example 16:9. This calculator does two jobs. First, given a target ratio and one known dimension, it computes the matching dimension so your image stays perfectly proportioned. Second, it takes any pixel size such as 1920×1080 and reduces it to its simplest ratio (16:9), telling you the proportions of a file you already have.
How to calculate the missing dimension
Pick a preset (16:9, 4:3, 21:9, 1:1, 3:2, 9:16, or cinematic 2.39:1) or type a custom ratio. Then enter the width you want, and the height is filled in automatically — or enter the height to get the width. The math is simply height = width × ratioHeight ÷ ratioWidth. For a 16:9 video at 1280 px wide, the height works out to 720 px.
How to reduce pixels to a ratio
Type a width and height into the reducer and it divides both by their greatest common divisor (GCD) to find the simplest whole-number ratio. 1366×768 reduces to roughly 16:9, while 1024×768 reduces to exactly 4:3. The tool also shows the decimal ratio (for example 1.778:1) and a friendly name when one matches.
Common aspect ratios and where they are used
- 16:9 — the standard for HD/4K video, YouTube, and most monitors and TVs.
- 4:3 — older displays, many tablets, and classic photography.
- 1:1 — square images for profile pictures and many social posts.
- 9:16 — vertical video for stories, Reels, and TikTok.
- 21:9 — ultrawide cinematic monitors and films.
Keeping the correct aspect ratio when resizing prevents the stretching and squashing that happens when width and height are scaled by different amounts. All calculations run in your browser.
What an aspect ratio calculator does
The aspect ratio is the proportional relationship between an image or screen's width and its height, written as two numbers separated by a colon — for example 16:9. This calculator does two jobs. First, given a target ratio and one known dimension, it computes the matching dimension so your image stays perfectly proportioned. Second, it takes any pixel size such as 1920×1080 and reduces it to its simplest ratio (16:9), telling you the proportions of a file you already have.
How to calculate the missing dimension
Pick a preset (16:9, 4:3, 21:9, 1:1, 3:2, 9:16, or cinematic 2.39:1) or type a custom ratio. Then enter the width you want, and the height is filled in automatically — or enter the height to get the width. The math is simply height = width × ratioHeight ÷ ratioWidth. For a 16:9 video at 1280 px wide, the height works out to 720 px.
How to reduce pixels to a ratio
Type a width and height into the reducer and it divides both by their greatest common divisor (GCD) to find the simplest whole-number ratio. 1366×768 reduces to roughly 16:9, while 1024×768 reduces to exactly 4:3. The tool also shows the decimal ratio (for example 1.778:1) and a friendly name when one matches.
Common aspect ratios and where they are used
- 16:9 — the standard for HD/4K video, YouTube, and most monitors and TVs.
- 4:3 — older displays, many tablets, and classic photography.
- 1:1 — square images for profile pictures and many social posts.
- 9:16 — vertical video for stories, Reels, and TikTok.
- 21:9 — ultrawide cinematic monitors and films.
Keeping the correct aspect ratio when resizing prevents the stretching and squashing that happens when width and height are scaled by different amounts. All calculations run in your browser.
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Frequently Asked Questions
Common questions about the Aspect Ratio Calculator
Select the 16:9 preset (or enter 16 and 9 as the ratio), then type your width in pixels. The height is calculated automatically using height = width x 9 / 16. For example, 1280 px wide gives 720 px tall.
Use the reducer card: enter the image's pixel width and height and the tool divides both by their greatest common divisor to give the simplest ratio. For instance, 1920x1080 reduces to 16:9 and 1024x768 reduces to 4:3.
16:9 is standard for HD video and most screens, 4:3 is used by older displays and classic photos, 1:1 is square (common on social media), 9:16 is vertical video for stories and Reels, and 21:9 is ultrawide cinematic.
If you scale width and height by different amounts, the image stretches or squashes and looks distorted. Calculating the matching dimension keeps the proportions identical so the result looks correct.
ℹ️ Disclaimer
This tool is provided for informational and educational purposes only. All processing happens entirely in your browser - no data is sent to or stored on our servers. While we strive for accuracy, we make no warranties about the completeness or reliability of results. Use at your own discretion.