Aspect Ratio Calculator

Calculate width or height to keep an aspect ratio, or simplify a ratio.

Given a new

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How it works

Enter an original width and height to define a ratio, then change either dimension and the tool solves for the other so the proportion stays the same. It also reduces the dimensions to their simplest whole-number ratio (for example 1920×1080 to 16:9) using the greatest common divisor. This keeps images, videos, and layouts from stretching when you resize them. All math runs locally in your browser with exact integer arithmetic where possible.


              newHeight = newWidth × (origHeight / origWidth)

Common use cases

  • Resizing an image to a new width without distorting it.
  • Finding the height for a 16:9 video at a given width.
  • Reducing pixel dimensions to a clean ratio like 4:3.

Frequently asked questions

How does it keep the ratio?

It divides the original height by the original width to get the ratio, then multiplies your new width by that ratio (or the inverse for height). The proportion stays identical.

Can it simplify a ratio?

Yes. It reduces width and height to their simplest whole-number form using the greatest common divisor, turning 1920×1080 into 16:9.

Does it round to whole pixels?

The computed dimension is rounded to the nearest pixel for practical use, with the exact value shown so you can decide how to round.