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Aspect ratio calculator
Reduce width and height to a ratio and calculate proportional dimensions.
02 / Your result
Your result will appear here.
Start with your own input or try an example.
What it does
Plan a proportional resize before editing an image or video. Enter the original width and height to find their reduced ratio, then supply a new width or height. The result includes proportional dimensions and the nearest whole-pixel size, with a note when rounding changes the proportions slightly. This tool calculates dimensions without uploading a file.
Useful when
- Find the height for a thumbnail at a fixed width.
- Check whether a graphic is 16:9, 4:3, or another ratio.
- Plan proportional dimensions for a banner or video frame.
How to use it
- Enter the original whole-number width and height in the same unit.
- Choose whether to set a target width or height and enter that dimension.
- Calculate the reduced ratio and scaled dimensions, then copy or download.
A few useful details
How is an aspect ratio reduced?
Width and height are divided by their greatest common divisor. For example, 1920 × 1080 reduces to 16:9. The order is always width first, then height.
Why are fractional and whole-pixel dimensions both shown?
A proportional resize can produce a fractional dimension. Raster images need whole pixels, so the tool also rounds to the nearest pixel and flags when this slightly changes the ratio.
Does it resize or crop my image?
No. It calculates dimensions only. Use the image resizer to process an image file. Inputs and scaled dimensions are limited to 1,000,000, and dimensions that would round to zero pixels are rejected.