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Simplify Aspect Ratio Calculator

Get the clean aspect ratio behind any pixel dimensions in a click.

How it is calculated

The tool reduces a width and a height to the smallest whole-number pair, as you would simplify a fraction. It rounds both values to whole numbers, finds their greatest common divisor (GCD) with Euclid's method, and divides both by it: ratio = (width ÷ GCD) : (height ÷ GCD). It also shows the decimal ratio width ÷ height with three decimals, using the numbers exactly as typed. Width and height can be pixels or any other unit, as long as both use the same one. Both must be above zero. The tool only simplifies; it does not match your ratio to the nearest standard format. A size such as 1366×768 has a GCD of 2 and gives 683:384, not 16:9, even though it is nearly 16:9. Use the decimal to compare such sizes.

Worked example

A video is 1920 pixels wide and 1080 high. The greatest common divisor of 1920 and 1080 is 120. Divide both: 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, so the ratio is 16:9. The decimal ratio is 1920 ÷ 1080 = 1.778. A vertical phone video of 1080 × 1920 gives 9:16 and 0.563. For 1366 × 768 the GCD is only 2, so the result is 683:384 with a decimal of 1.779, which is very close to 16:9 (1.778) but is not a clean pair.

Try this example →

Common mistakes

  • Expecting every screen size to reduce to a familiar ratio. Sizes such as 1366×768 give an awkward pair like 683:384, so compare the decimal to 1.778 instead.
  • Entering the sides in the wrong order. 1080:1920 is the portrait ratio 9:16, and the decimal 0.563 below 1 shows that.
  • Expecting 2560×1080 to show 21:9. The exact reduced ratio is 64:27, and 21:9 is only the marketing name for it.
  • Mixing units, such as a width in pixels and a height in inches. The ratio would mean nothing.
  • Entering decimal sizes and trusting the pair. The tool rounds to whole numbers before simplifying, so 1920.5 becomes 1921.

About this calculator

An aspect ratio is the ratio between a shape’s width and height, reduced to its simplest whole-number form the same way you would simplify a fraction — by dividing both numbers by their greatest common divisor. A 1920×1080 image, for instance, reduces to the familiar 16:9, while 1080×1080 reduces to 1:1 and 2560×1080 reduces to 64:27, which is marketed as ultrawide 21:9.

Video editors, photographers and app designers rely on aspect ratio constantly: choosing 16:9 for YouTube and most TVs, 9:16 for Instagram Reels and TikTok, 4:3 for older broadcast and some print formats, or 21:9 for cinematic widescreen. Getting the ratio right before you crop or export avoids black bars, stretched footage or awkward re-cropping later.

This calculator takes any pixel width and height, reduces them with the same divisor logic, and also gives you the decimal ratio so you can compare dimensions that do not simplify to a clean whole-number pair. The result is an exact reduction, so 1366×768 gives 683:384 (decimal 1.779), which is close to but not exactly 16:9.

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