Aspect Ratio Calculator
Calculate and maintain aspect ratios for images, videos, and screens. Find missing dimensions.
About this calculator
Find the aspect ratio of any width and height, or enter one new dimension and get the other so images and videos keep their shape.
Designers, video editors and developers use it to resize without stretching or cropping by accident.
How to use it
- Enter Width and Height, or choose a ratio preset.
- Change one side and read the other.
- Read the simplified ratio.
How it works
The aspect ratio is width divided by height, reduced to simplest terms using the greatest common divisor: 1920 × 1080 has GCD 120, so the ratio is 16:9. To scale, keep the ratio fixed: new height = new width × (original height ÷ original width). 1920 × 1080 scaled to a width of 1280 gives a height of 1280 × 1080 ÷ 1920 = 720.
Worked example
Common ratios
| 16:9 | HD/4K video, most monitors (1920×1080, 3840×2160) |
| 4:3 | Old TVs, iPad, presentations (1024×768) |
| 1:1 | Instagram posts (1080×1080) |
| 9:16 | Stories, Reels, Shorts (1080×1920) |
| 3:2 | DSLR photos, Surface laptops |
| 21:9 | Ultrawide monitors and cinema |
Everything runs in your browser. Nothing is uploaded.
Tips and common mistakes
- Lock the ratio when resizing, or images stretch.
- For social posts check each platform's current recommended size.
- Crop rather than stretch to change ratio.
- Round to whole pixels; fractional sizes blur.
- Use CSS aspect-ratio: 16/9 to keep embeds responsive.
Frequently asked questions
What is an aspect ratio?
The proportional relationship between width and height, written W:H.
How do I find the ratio of 1920×1080?
Divide both by their GCD, 120, to get 16:9.
How do I resize an image without distortion?
Keep the ratio fixed and change one dimension; compute the other.
What ratio is a phone screen?
Most modern phones are around 19.5:9 to 20:9.
What ratio is best for YouTube?
16:9.
What is the CSS aspect-ratio property?
It reserves space with a fixed ratio, such as aspect-ratio: 16/9.