Aspect Ratio Calculator
Calculate, simplify, and solve missing dimensions for any aspect ratio.
1920 × 1080
16:9
Common Aspect Ratio Presets
Standard
Social Media
Cinema
Understanding Aspect Ratios
An aspect ratio is the proportional relationship between a rectangle's width and height, expressed as two integers separated by a colon (e.g. 16:9) or as a decimal (≈ 1.7778). When resizing images or videos without distortion, both dimensions must maintain that ratio. To find a missing dimension, divide the known dimension by the ratio's corresponding part and multiply by the other part — this tool does that arithmetic automatically. The simplification uses the greatest common divisor (GCD), so 1920×1080 correctly reduces to 16:9 rather than staying as 1920:1080. All math runs locally in your browser.
Related tools: Image Resizer · Image Compressor
Built and maintained by Meet Shah · Last updated
What this tool is used for
- Solving a height from a width at a target ratio.
- Checking whether a set of dimensions matches a standard ratio.
- Working out crop dimensions for a required ratio.
- Converting a ratio into pixel dimensions for an export.
- Comparing two ratios that look similar, such as 16:9 against 1.85:1.
Frequently Asked Questions
- How is an aspect ratio reduced?
- By dividing both dimensions by their greatest common divisor. 1920×1080 has a GCD of 120, giving 16:9. That is why the tool reports a clean ratio for standard sizes and an awkward one for arbitrary dimensions — the arithmetic is exact, not approximate.
- Why is 16:9 the standard?
- Because it is the geometric mean of the formats it had to accommodate — 4:3 television and the 2.35:1 of widescreen cinema. Kerns Powers derived it in the 1980s specifically so that both could be shown with the least wasted area, which is why the number is not round.
- What does 21:9 actually mean?
- It is marketing shorthand rather than a ratio. Common ultrawide panels are 2560×1080 (64:27, about 2.37:1) and 3440×1440 (43:18), neither of which is 21:9 exactly. The label persists because 64:27 does not sell as well.
- How do I keep an aspect ratio while resizing?
- Scale both dimensions by the same factor, which is what the calculator solves for when you fix one side. In CSS the `aspect-ratio` property does it declaratively, which also reserves the space before an image loads and prevents layout shift.
- What are non-square pixels?
- A legacy of analogue video, where the storage dimensions and the display dimensions differed — DVD's 720×480 displays as 16:9 because the pixels are wider than they are tall. It is why old footage looks stretched when treated as square-pixel data.
Common errors and gotchas
- Rounding to whole pixels and drifting off the exact ratio, which shows on a long dimension.
- Confusing a ratio with a resolution, where many resolutions share one ratio.
- Mixing up which term is width and which is height.
- Ignoring device pixel ratio, so the exported asset is half the resolution needed.
- Assuming a nominal ratio such as 16:9 is exact for a given display, which it often is not.