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Aspect Ratio Calculator

How do I calculate aspect ratio?

How it is calculated

The tool keeps the proportion between width and height and solves for the missing side: h₂ = w₂ × h₁ / w₁. Enter the original width w₁ and height h₁, plus the new width w₂, in any one unit such as pixels. It also shows the simplified ratio by dividing both original sides by their greatest common divisor. When w₁ or h₁ is a decimal, it shows the ratio as w₁/h₁ : 1 to two decimals instead. All three values must be greater than zero. The new height is not rounded to a whole number beyond two decimals, so for images you need to round to whole pixels yourself.

Worked example

An image of 1920 × 1080 is to be resized to a width of 1280. The new height is 1280 × 1080 / 1920 = 720.00. The greatest common divisor of 1920 and 1080 is 120, so the ratio is 1920/120 : 1080/120 = 16:9.

Try this example →

Common mistakes

  • Entering the new width in a different unit than the original, such as inches against pixels.
  • Typing the new height in the width field: the tool solves only for height.
  • Rounding the ratio, so that 1.78:1 is treated as an exact 16:9 when it is only close.
  • Forgetting to round the calculated height to a whole pixel, which can leave a one pixel stretch.
  • Swapping width and height of the original, which turns a landscape ratio into portrait.

About this calculator

This tool keeps a width-to-height ratio fixed while solving for a missing dimension — enter a known width and height plus a new width, and it returns the matching height that preserves the same proportions, along with the ratio in its simplest form (like 16:9 or 4:3).

It is a staple for video editors and YouTubers resizing footage without distortion, designers cropping images or laying out responsive layouts, and anyone printing or resizing a photo who needs to know what height goes with a given width so nothing gets stretched or squashed.

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  • Editorial team

    When picking a target width, look for one that gives a whole-number height so you avoid fractional pixels. Resizing 1920 by 1080 to 1280 gives a clean 720, while a width of 1000 gives 562.50. Many video encoders also prefer even dimensions, so check the height is even as well. Which formats or platforms are you resizing for?

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