What Is an Aspect Ratio Calculator?
An Aspect Ratio Calculator tells you the proportional relationship between a width and height — expressed as a simplified ratio like 16:9, 4:3, or 1:1. It also lets you scale one dimension while keeping the same ratio, so you can resize images, videos, or layouts without distortion.
All calculations happen locally in your browser using pure JavaScript. Nothing is sent to a server.
How to Use
- Enter width and height — the ratio appears instantly, simplified to lowest terms
- Use a preset — click 16:9, 4:3, 1:1, 21:9, 9:16, 3:2, or 5:4 to pre-fill the ratio
- Scale to a new size — enter a new width or height in the scaling section; the missing dimension is calculated automatically
- Copy the result — click Copy to get the formatted string, e.g.
1920 × 1080 (16:9)
Common Aspect Ratios
| Ratio | Typical Use |
|---|---|
| 16:9 | HD/FHD/4K video, most monitors, YouTube |
| 4:3 | Older monitors, SD video, some cameras |
| 1:1 | Instagram posts, profile pictures, square formats |
| 21:9 | Ultrawide monitors, cinematic video |
| 9:16 | Vertical video, Instagram Stories, TikTok |
| 3:2 | DSLR/mirrorless camera sensors, 35 mm film |
| 5:4 | Older square-ish monitors (e.g. 1280×1024) |
How the GCD Algorithm Works
The calculator divides both dimensions by their Greatest Common Divisor (GCD) using the Euclidean algorithm. For 1920×1080:
- GCD(1920, 1080) = 120
- 1920 ÷ 120 = 16
- 1080 ÷ 120 = 9
- Result: 16:9
This always produces the smallest whole-number ratio that exactly represents the proportions.
Standard Video Resolutions
| Resolution | Width × Height | Ratio |
|---|---|---|
| HD 720p | 1280 × 720 | 16:9 |
| Full HD 1080p | 1920 × 1080 | 16:9 |
| QHD 1440p | 2560 × 1440 | 16:9 |
| 4K UHD 2160p | 3840 × 2160 | 16:9 |
Scaling Without Distortion
To resize an image while keeping its aspect ratio, only one dimension needs to change — the other follows automatically:
- New height from width: height = (newWidth ÷ ratioWidth) × ratioHeight
- New width from height: width = (newHeight ÷ ratioHeight) × ratioWidth
The tool rounds to the nearest whole pixel.
Privacy
All calculations run entirely in your browser. No dimensions or results are ever transmitted to a server.