Aspect Ratio Calculator
Reducing a Resolution to Its Simplest Ratio
An aspect ratio is just a width-to-height fraction reduced to its lowest terms, the same way you'd simplify 4/8 to 1/2. Video and display marketing rounds this to familiar labels like "16:9" or "21:9," but the exact simplified fraction of a real resolution doesn't always match the marketing name precisely. This calculator reduces any width and height to their true simplified ratio, or works in the other direction — solving for a missing width or height once a target ratio is fixed.
The Formula
Simplifying scales both dimensions to integers and divides out their greatest common divisor; solving for a missing side uses the ratio directly:
Height = Width × (RatioHeight / RatioWidth)
Width = Height × (RatioWidth / RatioHeight)
Reducing by the greatest common divisor is what turns a resolution like 1920×1080 into the compact 16:9 most people recognize.
Where Aspect Ratio Matters
- Video editing and export — matching a project's aspect ratio to the target platform (16:9 for YouTube, 9:16 for vertical mobile video) before cropping or padding is added.
- Responsive image layouts — reserving the correct width/height ratio in a webpage layout so images don't cause content to jump as they load.
- Print and framing — scaling a photo to a specific print size without distorting it means keeping the original ratio intact.
- Display shopping — recognizing that a "21:9" ultrawide monitor's true resolution ratio is often a slightly different simplified fraction than the marketing name suggests.
Common Resolutions and Their Exact Simplified Ratio
| Resolution | Simplified Ratio | Common Name |
|---|---|---|
| 1024 x 768 | 4:3 | XGA |
| 1280 x 720 | 16:9 | HD |
| 1920 x 1080 | 16:9 | Full HD |
| 2560 x 1440 | 16:9 | QHD |
| 3840 x 2160 | 16:9 | 4K UHD |
| 2560 x 1080 | 64:27 | Marketed as "21:9" |
| 3440 x 1440 | 43:18 | Marketed as "21:9" |
Ultrawide monitors marketed as "21:9" rarely simplify to exactly 21:9 — 2560x1080 and 3440x1440 both reduce to a different exact fraction, close to but not identical to 21:9.
How to Use This Calculator
- Choose a calculation type: Simplify Ratio from Width/Height, Find Height from Ratio, or Find Width from Ratio.
- For simplifying, enter Width (px) and Height (px).
- For the other two modes, enter the known dimension plus Ratio Width and Ratio Height (for example, 16 and 9).
- Select Calculate to get the simplified ratio or the missing dimension.
Related Calculations
Solving for a full screen size instead of just the ratio? Use the Screen Size Calculator. Working with video storage/display pixel shapes rather than screen ratios? See the Pixel Aspect Ratio Calculator.