How to calculate an aspect ratio
Is this artwork 16:9 or 4:3? What height should a 1280-pixel-wide video export be? Aspect-ratio questions are really one division and a greatest common divisor — enter the two dimensions and get the simplified ratio, the decimal value, and proportional target dimensions.
Step by step
Open the aspect-ratio calculator
Start the free calculator — the math runs in your browser.
Enter the width and height
Type the source dimensions, such as a 1920 × 1080 video frame; both must be greater than zero.
Read the simplified ratio
The dimensions are reduced by their greatest common divisor — 1920 × 1080 simplifies to 16:9 with a decimal ratio of 1.7778.
Enter a target width
Type the width you are scaling to, such as 1280 for a smaller video export.
Get the matching height
The proportional height comes back instantly: 1280 wide becomes 1280 × 720, with no distortion.
Tips that save a second try
Ratio describes shape, not quality: a 160 × 90 image and a 3840 × 2160 image are both 16:9, but only one is sharp on a big screen.
The simplified ratio uses dimensions rounded to integers, so fractional sources can yield a ratio that does not exactly describe the original decimals.
The resizer solves from a target width only — to crop to a ratio instead, use the image cropper's presets.
Common questions
Does matching the ratio guarantee the same image quality?
No. Aspect ratio describes shape, not resolution, compression, or sharpness. A 160×90 image and a 3840×2160 image are both 16:9.
Why must width and height be greater than zero?
A zero or negative dimension cannot describe a usable rectangular frame or produce a finite width-to-height ratio.