Leave the new height empty and it is worked out for you.
Set to 0 to calculate it from the width.
Results are rounded to whole pixels. Very small images may be off by one pixel, which is unavoidable. Check the platform documentation for the exact frame size it expects.
Calculated entirely in your browser. Nothing you enter is sent anywhere.
How to use it
Start from a preset or enter your own
Presets cover HD, 4K, vertical, square and ultrawide.
Fill in one new dimension
Leave the other at zero and it is worked out for you.
Check the verdict
It tells you whether proportions are kept, and how large the bars would be if not.
How the calculation works
An aspect ratio is the relationship between width and height. It describes shape rather than size: 1920x1080 and 1280x720 are different sizes but the same shape.
The ratio is reduced using the greatest common divisor, so 1920x1080 becomes 16:9 rather than 1920:1080. When one new dimension is supplied, the other is derived by multiplying or dividing by that same ratio.
The letterbox option matters for video. If the target frame is a different shape, you either crop or you add bars, and the calculator tells you exactly how thick those bars would be rather than leaving you to guess.
What this calculator does not do
Results are rounded to whole pixels, so very small images can be off by one. That is unavoidable, because there is no such thing as half a pixel.
It does not resize anything. It gives you the numbers to type into whatever tool actually does the work.
It cannot tell you which ratio to use. That depends on where the video is going, and the platform documentation is the right source.
Questions
What is the most common video ratio?
16:9 for almost everything on desktop and television. 9:16 for vertical phone video. 1:1 still appears in some feeds.
Why does it say distorted?
Because the width and height you entered do not divide to the same ratio as the original. Clear one field and let it be calculated.
Letterbox or crop?
Letterbox keeps the whole frame and adds bars. Crop fills the frame and loses the edges. Which is right depends on what is at the edges.
Does upscaling lose quality?
Enlarging past the original pixel dimensions always softens an image. The ratio stays correct but the detail is not there to recover.
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