Aspect Ratio Calculator
Find the size that keeps your proportions, and identify what ratio a size actually is.
Ratio locked — change one dimension and the other follows.
Aspect ratio
16:9
Exact ratio
16:9
Fully reduced
Resolution
2.07 MP
2,073,600 px
Set a ratio
Common sizes
About this tool
The aspect ratio calculator answers the two questions that come up constantly when working with images: "if I scale this to 1200 wide, how tall should it be so it isn't stretched?" and "what ratio is this size, actually?"
The ratio lock is built so proportions cannot drift. It remembers the ratio at the moment you locked it and always computes from that, rather than from the already-rounded numbers on screen — unlike tools that recompute from the latest values, where typing back and forth slowly walks the shape away from where it started.
The identification half deliberately gives a usable answer. 1366×768 reduces exactly to 683:384, which is entirely correct and completely unhelpful, so it is reported as approximately 16:9 with the exact reduction shown next to it.
The presets cover the sizes people actually export for: YouTube video, social posts and stories, link-preview images, and A4 at 300 dpi for print.
How to use
- 1Enter the width and height of your source image
- 2Leave the ratio locked and change one dimension — the other follows
- 3Or click a ratio like 16:9 to fit the height to the width you have
- 4Use the presets for YouTube, Instagram or link-preview sizes
Frequently asked questions
- Why is a ratio sometimes marked approximate?
- Some sizes do not reduce tidily. 1366×768 reduces to 683:384 — correct, and no use to anyone — so it is reported as approximately 16:9, with the exact reduction shown alongside.
- How does the ratio lock work?
- It remembers the ratio as it was when you locked it and always computes from that, rather than from the already-rounded numbers on screen. So the proportions do not drift as you type back and forth.
- What is the difference between 16:9 and 4:3?
- 16:9 is the widescreen shape of modern video and TV; 4:3 is the older screen and camera shape. Put 4:3 content in a 16:9 frame and you get bars down the sides — or a stretched, distorted image if you fill it.
- Why are the results always whole numbers?
- Real image dimensions are whole pixels, so results are rounded. That can shift the ratio by under a pixel, which is not visible.
- What does the MP figure mean?
- Total pixels in millions (megapixels). Useful for comparing the resolution of different sizes and estimating file size.