Aspect Ratio Calculator
Simplify any width × height to its aspect ratio (1920×1080 → 16:9) and calculate the missing width or height when resizing images, video or screens.
Enter a new width or height to get the other side at the same ratio.
Results
What is Aspect Ratio Calculator?
Enter a width and height to get the simplified aspect ratio (for example 16:9) and its decimal form. Add a new width or height and the tool calculates the other side so the proportions stay the same.
How to use Aspect Ratio Calculator
- Enter the original Width and Height, or click a preset such as 16:9 or 4:3.
- Read the simplified Aspect ratio, the decimal ratio and whether it is landscape or portrait.
- Type a New width (or New height) to get the matching other side.
Example
1920 × 1080, new width 1280
Aspect ratio 16:9, decimal 1.7778 : 1, new height 720
When to use Aspect Ratio Calculator
Use it when exporting video, cropping photos, sizing responsive embeds or checking a monitor resolution. Note that marketing names such as "21:9" are approximations: real ultrawide panels are 64:27 (2560×1080) or 43:18 (3440×1440), and the tool shows the exact reduced ratio.
How Aspect Ratio Calculator works
The ratio is reduced by dividing both sides by their greatest common divisor (Euclid's algorithm): 1920 and 1080 share a GCD of 120, giving 16:9. Decimal inputs are scaled by a power of ten first so 1.5 : 1 becomes 3:2. The missing side is solved by cross-multiplication: new height = new width × height ÷ width. Values are rounded to two decimals for display only.
Common Use Cases
- Finding the height of a 1280-pixel-wide 16:9 video
- Checking whether an image is 4:3, 3:2 or 16:10
- Resizing thumbnails without distortion
- Comparing screen resolutions
FAQs
Why does 2560×1080 show 64:27 instead of 21:9?
64:27 is the exact reduced ratio (2.370 : 1). "21:9" (2.333 : 1) is a rounded marketing name for the same class of ultrawide screens.
Can I use decimal values?
Yes. 1.85 × 1 is scaled to 185 × 100 and reduced to 37:20.
Does the new size have to be a whole number?
The tool shows two decimals. For pixels, round to the nearest whole number; for video encoders an even number is often required.