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Aspect Ratio Calculator

Find the aspect ratio of any width and height, or resize to a new width or height while keeping the same ratio, for screens, photos and video.

Results

ItemValue

Common sizes at this ratio

WidthHeight
Works with pixels, inches or any unit, as long as width and height use the same one. New sizes are rounded to the nearest whole pixel. Some screen ratios, like 21:9, are marketing names for sizes such as 2560 × 1080 (64:27).

Quick Answer

Aspect ratio = width ÷ height, written as the smallest whole numbers. 1920 × 1080 has a greatest common divisor of 120, so the ratio is 16:9. To keep 16:9 at a width of 1280, the new height is 1280 × 9 ÷ 16 = 720.

Last updated: 3 November 2026 ·How we calculate this: the greatest common divisor and proportional scaling

Table of Contents

How This Aspect Ratio Calculator Works

Enter a width and height to find their aspect ratio. The calculator divides both by their greatest common divisor to get the simplest ratio, such as 16:9, gives the decimal form and the nearest common ratio, and lists standard sizes with the same shape. Switch the mode to resize: enter a new width or height, and it finds the matching other side so the image does not stretch.

Quick explanation: aspect ratio is the shape of a rectangle.

  • 16:9: 16 units wide for every 9 tall, the standard widescreen shape.
  • Same ratio: 1280 × 720 and 3840 × 2160 are both 16:9.
  • Portrait: taller than wide, such as 9:16 phone video.

How to Use the Aspect Ratio Calculator

  1. Choose to find a ratio, or to resize by width or height.
  2. Enter the original width and height.
  3. For resizing, enter the new width or height.
  4. Press Calculate.
  5. Read the ratio, new size and common sizes.

Core Formulas

  • Ratio: (width ÷ GCD) : (height ÷ GCD)
  • New height: new width × height ÷ width
  • New width: new height × width ÷ height
  • Decimal ratio: width ÷ height, such as 1.778 for 16:9

Key Terms

  • Aspect ratio: the ratio of width to height.
  • GCD: greatest common divisor, used to simplify the ratio.
  • Resolution: the width and height in pixels.
  • Letterbox: black bars above and below a wide video on a narrower screen.
  • Pillarbox: black bars on the sides of a narrow video on a wide screen.

Worked Example

A photo is 4000 × 3000 pixels. What is its ratio, and how tall is it at 1200 pixels wide?

  • GCD of 4000 and 3000 is 1000, so the ratio is 4:3
  • New height = 1200 × 3000 ÷ 4000 = 900
  • So the resized photo is 1200 × 900

Real-Life Examples

  • YouTube thumbnails: 1280 × 720 is 16:9.
  • Phone video: 1080 × 1920 is 9:16 for Stories and Shorts.
  • Printing photos: a 3:2 photo fits a 6 × 4 inch print with no cropping.
  • Web design: keep image boxes at a fixed ratio so pages do not jump while loading.

Aspect Ratio vs Resolution

  • Aspect ratio: the shape, such as 16:9.
  • Resolution: the number of pixels, such as 1920 × 1080.
  • Link: many resolutions share one ratio. 720p, 1080p and 4K are all 16:9.

Common Aspect Ratios

RatioDecimalExample sizeUsed for
16:91.7781920 × 1080HD and 4K TVs, YouTube, most monitors
4:31.3331920 × 1440Older TVs, iPad, many cameras
3:21.5001920 × 128035 mm film, many DSLR photos
21:92.3331920 × 823Ultrawide monitors (marketing name)
1:11.0001920 × 1920Square social posts
9:160.5621080 × 1920Phone video, Stories, Reels, Shorts
4:50.8001536 × 1920Portrait social posts
16:101.6001920 × 1200Many laptops
1.85:11.8501920 × 1038Widescreen cinema
2.39:12.3901920 × 803Anamorphic cinema

Tips

  • Keep the ratio when resizing to avoid stretched or squashed images.
  • Crop to change the ratio, for example from 4:3 to 16:9.
  • Letterboxing: black bars appear when video and screen ratios differ.
  • Even numbers: many video encoders prefer even widths and heights.

To change a 4:3 photo into 16:9 without stretching, keep the full width and crop the height: a 4000 × 3000 photo becomes 4000 × 2250, cutting 750 pixels from the top and bottom together. To keep the full height instead, the width would need to grow, which is only possible by adding bars or background.

Common Mistakes to Avoid

  • Changing only one side. Scale both sides by the same factor.
  • Mixing units. Use pixels for both sides, or inches for both.
  • Expecting 21:9 to be exact. Ultrawide screens are often 64:27 or 43:18.
  • Ignoring orientation. 16:9 and 9:16 are different shapes.
  • Upscaling small images. Keeping the ratio does not add detail.

Frequently Asked Questions

Divide width and height by their greatest common divisor. 1920 × 1080 becomes 16:9.

16:9.

New height = new width × old height ÷ old width.

Sizes such as 1024 × 768, 1600 × 1200 and 640 × 480.

UHD 4K, 3840 × 2160, is 16:9.

Posts are often 1:1 or 4:5, and Stories and Reels are 9:16. Check the app's current guidance.

Many modern phones are about 19.5:9 or 20:9 in portrait use.

Usually not. 2560 × 1080 is 64:27, which is about 2.37:1.

Width ÷ height, such as 1.778 for 16:9.

Its ratio differs from the screen's ratio.

Yes. Any unit works if both sides use it.

About 1.618:1, a shape some designers like. It is close to 16:10.

References & Sources

SourceUsed ForLink
Wikipedia, Aspect ratio (image) Common image and screen aspect ratios. https://en.wikipedia.org/wiki/Aspect_ratio_(image)
Wikipedia, Display aspect ratio Aspect ratios used by TVs, monitors and phones. https://en.wikipedia.org/wiki/Display_aspect_ratio