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Aspect ratio calculator

An aspect ratio is the width and height divided by their greatest common divisor, so 1920 × 1080 is 16:9. Enter a size to get its ratio, or a ratio and one side to get the other side, plus the CSS aspect-ratio value to copy.

px
px

Aspect ratio of 1920 × 1080

16:9

1.7778:1

16:9
Lowest terms
16:9
Decimal (width ÷ height)
1.7778:1
Nearest common ratio
16:9 (exact)
CSS
aspect-ratio: 16 / 9;
Orientation
Landscape

How do you calculate an aspect ratio?

Divide the width and the height by their greatest common divisor. For 1920 × 1080 the greatest common divisor is 120, so the ratio is 1920 ÷ 120 : 1080 ÷ 120 = 16:9. The decimal form is width ÷ height: 1.7778:1.

Many real screen sizes don't reduce to a familiar ratio. 1366 × 768 reduces only to 683:384, about 0.05% wider than 16:9, so the calculator calls it approximately 16:9 and gives both CSS values. It says "approximately" only within 2% of a common ratio.

To find a missing side, scale the ratio: height = width × H ÷ W, and width = height × W ÷ H. At 16:9 a 1280 px wide box is 1280 × 9 ÷ 16 = 720 px tall. Results are rounded to whole pixels, with the exact value shown when it isn't whole.

In CSS, aspect-ratio: 16 / 9 gives a box that shape, and a single number such as aspect-ratio: 2 means 2 / 1. MDN notes it only has an effect when at least one of the box's width or height is automatic.

ratio  = (width ÷ gcd) : (height ÷ gcd)
height = width × H ÷ W
width  = height × W ÷ H

What are the common aspect ratios and where are they used?

Common aspect ratios with an example size of each; decimals computed by this calculator, uses from the sources below
RatioDecimalExample sizeWhere it's used
1:11:11080 × 1080Square. Google Search requires favicons to be square (1:1), and its Article image guidance lists 1x1 among three ratios.
4:31.3333:11024 × 768One of the three image ratios Google recommends for Article structured data, with 16x9 and 1x1.
3:21.5:12304 × 1536Microsoft calls the Surface Laptop display 3:2; the 13.8-inch screen is 2304 × 1536.
16:101.6:12560 × 1600The MacBook Air (M1, 2020) display is 2560 × 1600.
16:91.7778:11920 × 1080YouTube's standard ratio on a computer; YouTube lists 1920 × 1080 for 1080p and 3840 × 2160 for 4K.
1.91:11.91:11200 × 630 (1.9048:1)Link-preview images: Meta asks for images as close to 1.91:1 as possible and at least 1200 × 630.
21:92.3333:12520 × 1080LG's 34-inch UltraWide FHD monitor is 2560 × 1080, which is 64:27 (2.37:1): approximately 21:9, not exactly.
9:160.5625:11080 × 1920Vertical video. YouTube says it may add padding around 9:16 vertical videos in computer browsers.

How to calculate an aspect ratio

  1. 1
    Choose what to work outPick the ratio of a width and height, or the missing side from a ratio.
  2. 2
    Enter the size or the ratioType a width and height in pixels, or a ratio such as 16:9, 4/3 or 1.91 with the side you know and its length.
  3. 3
    Read the ratio or the missing sideYou get the ratio in lowest terms, its decimal and the nearest common ratio, or the other side rounded to whole pixels with its exact value.
  4. 4
    Copy the CSSCopy the aspect-ratio line, or the size, straight into your stylesheet or design tool.

Frequently asked questions

What aspect ratio is 1920 × 1080?
16:9. The greatest common divisor of 1920 and 1080 is 120, and 1920 ÷ 120 = 16 while 1080 ÷ 120 = 9. 1280 × 720 and 3840 × 2160 are 16:9 too.
Is 1366 × 768 a 16:9 resolution?
Approximately, not exactly. It reduces to 683:384, or 1.7786:1, against 1.7778:1 for 16:9, a difference of about 0.05%.
How do I calculate height from width and aspect ratio?
Multiply the width by the ratio's second number and divide by its first: at 4:3, 800 px wide is 800 × 3 ÷ 4 = 600 px tall. Choose "Missing side from a ratio" above to do it for any ratio.
What is the aspect ratio of 1200 × 630?
Exactly 40:21, or 1.9048:1, which is approximately 1.91:1. A true 1.91:1 image 1200 px wide would be 628 px tall; Meta recommends at least 1200 × 630 and a ratio as close to 1.91:1 as possible.
How does the CSS aspect-ratio property work?
It gives a box a preferred width-to-height ratio, written aspect-ratio: 16 / 9; with a single number the height part defaults to 1. It only takes effect when at least one of the box's width or height is automatic.

Sources

Built and maintained by CountryDevs. Updated October 2026. Runs in your browser; what you type is not sent to us.

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