Aspect Ratio Calculator — Scale Dimensions and Find Missing Size
Calculate the aspect ratio from any width and height, scale dimensions while keeping the ratio, or find a missing width or height from a known ratio. Includes common video and social media presets.
Last updated: June 2026
- Aspect ratio
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- Decimal
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- Closest common ratio
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Original size
New size (enter one, the other fills in)
Aspect ratio
Known dimension (enter one, the other fills in)
Social media size reference
| Platform | Format | W × H (px) |
|---|---|---|
| Square | 1080×1080 | |
| Story | 1080×1920 | |
| YouTube | Thumbnail | 1280×720 |
| Cover | 820×312 | |
| Twitter / X | Header | 1500×500 |
| Banner | 1584×396 | |
| TikTok | Video | 1080×1920 |
About this tool
Work out any aspect ratio in seconds
The aspect ratio of an image or video is the relationship between its width and its height, written as two numbers like 16:9. It describes the shape of the frame regardless of its size, which is why a tiny thumbnail and a huge billboard can share the same ratio. This calculator handles the three questions you actually run into: what is the ratio, how do I resize without distortion, and what is the missing dimension?
The Calculate Ratio mode turns any width and height into the simplest whole-number ratio, the exact decimal, and the closest standard ratio it matches. The Scale Dimensions mode keeps your proportions locked while you change one side, so resizing a photo or export never stretches it. The Find Missing mode starts from a ratio like 16:9 and a known width or height and gives you the other number.
Presets cover the ratios you use most, from 16:9 video to 1:1 and 9:16 for social, and the reference table lists exact pixel sizes for Instagram, YouTube, Facebook, X, LinkedIn and TikTok. Everything updates instantly in your browser with nothing uploaded, so it is a quick, private companion to the image resizer and cropper when you are preparing graphics for a specific placement.
How it works
Three quick steps — no account, nothing uploaded to a server.
Pick a mode
Calculate a ratio, scale a size, or find a missing dimension.
Enter your numbers
Type width and height, or a ratio and one known side.
Read the result
Get the ratio or the missing dimension instantly.
FAQ
Frequently asked questions
How do I calculate an aspect ratio from width and height?
Enter the width and height in the Calculate Ratio tab and the tool divides them down to their simplest whole-number form using the greatest common divisor. For example, 1920 by 1080 simplifies to 16:9. It also shows the decimal ratio (1.7778) and tells you the closest common ratio it matches.
How do I resize an image while keeping the same ratio?
Use the Scale Dimensions tab. Enter the original width and height, then type either a new width or a new height. The tool fills in the matching dimension so the proportions stay identical, which is exactly what you want when resizing a photo or video without stretching it.
What is the difference between 16:9 and 4:3?
16:9 is the widescreen ratio used for HD, Full HD and 4K video, modern TVs and most monitors. 4:3 is the older, more square ratio used by traditional monitors and older TVs. The aspect ratio describes the shape of the frame, not its size, so a 16:9 image is always wider relative to its height than a 4:3 one.
What aspect ratio should I use for social media?
It depends on the placement: 1:1 for an Instagram square post, 4:5 for an Instagram portrait, 9:16 for Stories, Reels, TikTok and YouTube Shorts, and 16:9 for a YouTube thumbnail or standard video. The reference table on this page lists the exact pixel sizes for the most common platforms.
Is the aspect ratio calculator free?
Yes, completely. There is no sign-up, no limit and no cost. Every calculation runs in your browser, so nothing you enter is uploaded, and you can use all three modes and the presets as much as you like.
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