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Aspect Ratio Calculator

Calculate and scale aspect ratios for images and screens

Calculate Aspect Ratio

Optional: Enter new width or height to scale proportionally

Method and source check

Last checked:

Automated source and implementation review, including worked examples and documented numerical limits. This review does not provide professional advice or specialist approval.

Method

Reduce width:height to a simple ratio. If a positive new width or height is entered, scale the other dimension in proportion and round it to a whole pixel.

ratio = width:height reduced by gcd(width,height)

new height = round(new width × height/width)

Variables and units

width,height
positive original dimensions
new width/new height
optional positive target dimension

Worked example

For 1920×1080, ratio is 16:9; target width 1280 gives target height 720.

Limitations

Decimal ratio is rounded to three places; computed target dimension is rounded to the nearest whole pixel.

  • Whole-pixel rounding can slightly change the exact ratio.
  • Only one target dimension is used; if both are entered, width takes precedence under current behavior.
  • 16:9 is preserved exactly by scaling 1920×1080 to 1280×720.
  • For 3×2 at target width 5, rounded height 3 makes the displayed 5×3 an approximation.
  • For 1920×1080, target width 1280 or target height 720 both display the complete scaled pair 1280×720.

Sources

Table of Contents

How to Use

  1. Enter the original width and height
  2. Optionally enter a new width or height to scale proportionally
  3. View the simplified ratio and scaled dimensions

Calculate and scale aspect ratios for images and screens

Calculate aspect ratios and scale dimensions proportionally. Method: Reduce width:height to a simple ratio. If a positive new width or height is entered, scale the other dimension in proportion and round it to a whole pixel.

Maintaining aspect ratio is crucial when resizing images or videos to prevent distortion and ensure visual quality.

Common Aspect Ratios

Aspect RatioCommon UseExample Resolution
16:9Widescreen HD video, modern TVs1920×1080 (Full HD)
4:3Traditional TV, older monitors1024×768
64:27Ultra-wide monitors, cinema2560×1080
1:1Square images, Instagram posts1080×1080
3:235mm film, DSLR cameras3000×2000
9:16Vertical video, mobile stories1080×1920

How to Calculate Aspect Ratio

To calculate aspect ratio, divide both width and height by their greatest common divisor (GCD):

  • Find the GCD of width and height
  • Divide width by GCD to get the first number
  • Divide height by GCD to get the second number
  • Express as width:height

Example: For 1920×1080, GCD is 120. 1920÷120 = 16, 1080÷120 = 9, so the aspect ratio is 16:9.

Worked scenario

Photography & Video

  • 1920×1080 → 16:9; width=1280 → height=720.

Web & App Design

  • 1200×800 → 3:2; width=600 → height=400.

Display & Screens

  • 3840×2160 → 16:9; width=1920 → height=1080.

Method, example, rounding, and limits

Method: Reduce width:height to a simple ratio. If a positive new width or height is entered, scale the other dimension in proportion and round it to a whole pixel.

Worked example: 1920×1080 → 16:9; Wnew=1280 → Hnew=720.

Rounding: The decimal ratio uses three decimal places; the calculated target dimension is rounded to a whole pixel.

Limit: Whole-pixel rounding can slightly change the exact ratio.

Reference: OpenStax. https://openstax.org/books/contemporary-mathematics/pages/5-4-ratios-and-proportions

Frequently Asked Questions

What's the difference between 16:9 and 4:3 aspect ratios?
16:9 is a widescreen format used in modern TVs and monitors, providing a wider viewing area. 4:3 is the traditional format used in older TVs and monitors, appearing more square-shaped.
Will changing aspect ratio distort my image?
If you crop or resize to a different aspect ratio, you'll either need to crop parts of the image or add letterboxing (black bars). To avoid distortion, always scale proportionally using the same aspect ratio.
How do I maintain aspect ratio when resizing?
Calculate the scaling factor by dividing the new dimension by the original dimension, then apply that factor to both width and height. The calculator applies this scaling when you enter a new width or height, then rounds the calculated dimension to a whole pixel. Rounding can slightly change the exact ratio.
What aspect ratio should I use for social media?
Choose a ratio to fit the frame: 16:9 is horizontal, 9:16 is vertical, and 1:1 is square. If your source has a different ratio, crop it or add padding to fit without stretching. Check the destination's current size and ratio requirements before exporting.

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