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Aspect Ratio Calculator

Simplify a width and height, or find a missing side

16:9
Decimal: 1.7778

About Aspect Ratio Calculator

Aspect Ratio Calculator reduces a width and a height to the smallest whole-number ratio and gives the decimal value (width divided by height, up to four decimals). Decimals are accepted and scaled first, so 2.39 and 1 give 239:100. Two extra fields answer the usual resizing question: type a new width to get the matching height, or a new height to get the width; when the answer is not a whole pixel, the exact value is shown next to the rounded one. Five presets load common sizes. Values must be positive numbers; anything else shows a dash instead of a ratio.

Example

A laptop screen size resized to a width of 1280, computed with the page's own code.

Typed in the fields

Width: 1366
Height: 768
New width → height: 1280

Shown by the calculator

683:384
Decimal: 1.7786
Height: 720 (≈ 719.648609, rounded)

How to calculate an aspect ratio and a missing side

  1. 1Type the original size in "Width" and "Height", or pick one of the "Common presets" such as 16:9 (1920×1080).
  2. 2Read the simplified ratio and the "Decimal" value; both change as you type.
  3. 3To resize, type the new width in "New width → height", or the new height in "New height → width".
  4. 4Read the result under that field: the value rounded to a whole pixel, followed by the exact value when it is not whole.

Formats and limits

Accepted values
Positive numbers, including decimals (2.35) and exponent form (1e3); zero, negative, or empty values give no ratio
Results
Simplified ratio, decimal ratio to four decimal places, and the missing side rounded to a whole pixel
Presets
16:9 (1920×1080), 4:3 (1024×768), 1:1 (1080×1080), 21:9 (2560×1080), 9:16 (1080×1920)

Where your numbers are processed

The ratio and the missing side are computed by the page itself each time you type a digit. Your numbers are not sent to our servers or to anyone else, and nothing is saved: after a reload the fields go back to 1920 and 1080 and the resize fields are empty.

Frequently asked questions

Can it keep the aspect ratio when I resize an image?

Yes. Enter the original width and height, then type the new width in "New width → height": the height shown keeps the same proportions. For example, 1366 by 768 resized to a width of 1280 needs a height of 720, rounded from about 719.65 (the page shows ≈ 719.648609).

Is 1366 by 768 exactly 16:9?

No. 1366 divided by 768 is 1.7786, while 16:9 is 1.7778, so the calculator shows 683:384. It reduces the exact numbers you type and never rounds them to the nearest common ratio.

Can I enter decimal values such as 2.39 and 1?

Yes. Both values are scaled to whole numbers before they are reduced, so 2.39 and 1 give 239:100 with a decimal of 2.39. Exponent form such as 1e3 is read too; zero, negative, or empty values show a dash.

Can I use the decimal value in CSS?

Yes. It is the width divided by the height, rounded to four decimal places, and the CSS aspect-ratio property accepts a single number, for example aspect-ratio: 1.7778. CSS also accepts the ratio itself written as 16 / 9.

Tips and tricks

  • ✓Picking a preset replaces both "Width" and "Height", so type your own size again before resizing.
  • ✓Once you know the target size, Resize Image or Crop Image can produce the image itself.

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