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Aspect Ratio Calculator

Find the aspect ratio of any width and height, and the matching height for a new width.

By Nitin Raturi · Last reviewed

Your worksheet

How to use the Aspect Ratio Calculator

Find the shape of a screen, image or video, and resize it without stretching.

  1. Enter the original width and height.
  2. Enter the new width you want.
  3. Read the ratio, the new height and the closest common shape.

Good to know

  • Portrait sizes give ratios like 9:16.

Ratio = width : height reduced. New height = new width × height ÷ width.

Width

The original width, in pixels, centimetres or any unit.

How to fill it in

  • Enter a number above 0; decimals are fine.

Example

A 6000 × 4000 camera photo is 3:2.

Height

The original height, in the same unit as the width.

How to fill it in

  • Enter a number above 0.

Example

A 2560 × 1080 ultrawide is 64:27, close to 21:9; 1366 × 768 reduces to 683:384.

New width

The width you want, to find the matching height.

How to fill it in

  • Use the same unit as above.

Example

1920 × 1080 at 1280 wide is 720 high; a 1080 × 1920 phone video at 720 wide is 1,280 high.

Aspect ratio

16:9

1,920 × 1,080 is 16:9 (1.7778:1). At a width of 1,280 the height is 720.00.

As a decimal
1.7778:1
Height at width 1,280
720.00
Closest common shape
16:9 (exact)

Ratios are reduced exactly; a new height that is not a whole number of pixels has to be rounded, which slightly changes the shape.

ChangelogHow we test this calculatorEmbed this calculator

How this calculator works

  1. Step 1Ratiowidth : heightCompare the two sides.
  2. Step 2Reduce÷ greatest common divisorLowest whole numbers.
  3. Step 3Resizenew w × h ÷ wKeep the same shape.

Aspect ratio is the shape of a rectangle: width compared with height. Two screens of different sizes look the same shape when their ratios are equal.

To resize without stretching, keep the proportion: the new height is the new width times the original height divided by the original width.

Worked example: Full HD to 1280 wide

1920 × 1080 scaled to a width of 1280
New height
new width × height ÷ width
  1. Greatest common divisorGCD(1920, 1080)120
  2. Ratio1920 ÷ 120 : 1080 ÷ 12016:9
  3. New height1280 × 1080 ÷ 1920720

Read the result

  • Camera photo 6000 × 40003:2
  • Full HD 1920 × 108016:9
  • Ultrawide 2560 × 108064:27
Width ÷ height of common sizes

Some “16:9” sizes are not exact: 1366 × 768 reduces to 683:384, a shade off 16:9.

  • 1920 × 108016:9Landscape video and most TVs.
  • 1080 × 19209:16Phone video; at 720 wide it is 1,280 high.

Assumptions and limits

  • Any unitPixels, inches or centimetres.
  • Whole pixelsRound the new height for images.
  • No croppingChanging ratio needs cropping or bars.
  • Square pixelsAssumes pixels are square.

An aspect ratio is a ratio of width to height.

To resize an image to the new dimensions, use the image resizer. For general ratios, the ratio calculator simplifies and scales them.

Common mistakes

  • Mistake: Changing width and height by the same amount.

    Instead: Change them by the same factor.

  • Mistake: Assuming 21:9 monitors are exactly 21:9.

    Instead: 2560 × 1080 is 64:27.

Checking the method

A separate script reduces every ratio with exact fractions and cross-multiplies the proportion, and matches each golden value.

Read how we test our calculators, or browse more everyday tools.

Frequently asked questions

What is the aspect ratio of 1920 × 1080?

16:9. At 1280 wide the matching height is 720.

Is 1366 × 768 exactly 16:9?

No, it reduces to 683:384, slightly different from 16:9.

What ratio is a 2560 × 1080 monitor?

64:27, marketed as 21:9.

How do I resize a phone video to 720 wide?

A 1080 × 1920 video at 720 wide is 1,280 high (9:16).

Does it work in centimetres?

Yes. Any unit works as long as width and height use the same one.

Sources and methodology

The formulas are standard time-value-of-money results. We check every figure against golden values worked out independently, by closed form and by month-by-month simulation; see the methodology.

Written and maintained by Nitin Raturi, a software engineer (about the author). Last reviewed 4 Nov 2026; next review due by . Found an error? Tell us.

Changelog

  • : Initial release.

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