Aspect Ratio Calculator

Enter any two values to calculate the third. Use presets for common video, social media and print sizes.

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Common presets

How to calculate aspect ratio

Enter any two of width, height and ratio — the calculator solves the third instantly, with presets for video, social media and print.

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1. Enter two values

Type a width and height (like 1920 × 1080), or a width and a target ratio like 16:9.

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2. Solve for the third

Pick whether to solve for width, height or ratio — the missing value is calculated instantly.

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3. Use a preset

One click for 16:9, 4:3, 21:9, 9:16 vertical video, Instagram 4:5 and common print sizes.

Aspect ratio = width divided by height. It decides whether a video letterboxes on YouTube (16:9), fills a phone screen for Reels and TikTok (9:16), or fits an Instagram feed (4:5). Resizing an image without keeping the ratio stretches it — calculate the matching height first with this tool, then resize with the Batch Image Resizer or crop precisely with the Image Cropper.

Aspect ratio FAQ

What is 16:9 in pixels?

Common 16:9 resolutions are 1280×720 (HD), 1920×1080 (Full HD), 2560×1440 (QHD) and 3840×2160 (4K). Any width × 9 ÷ 16 gives the matching height.

How do I resize an image without stretching it?

Keep the aspect ratio locked: divide the original width by height, then multiply the new width by that same ratio to get the new height. This calculator does that for you — enter the original ratio and your new width.

What aspect ratio is Instagram / TikTok / YouTube?

Instagram feed posts work best at 4:5 (1080×1350), Stories/Reels and TikTok at 9:16 (1080×1920), and YouTube at 16:9 (1920×1080). Square 1:1 (1080×1080) still works across most feeds.

What is the ratio of A4 paper?

A4 (210×297 mm) has a ratio of 1:1.414 (that is 1:√2) — the same ratio for every A-series paper size, which is why A4 folded in half is exactly A5.