How do I find the aspect ratio of an image?

Divide both the width and the height by their greatest common divisor (GCD). For example, a 1920x1080 image has a GCD of 120, giving 1920/120 : 1080/120 = 16:9. If you only know one ratio component, you can multiply by any common factor to get equivalent pixel sizes. This calculator does the division automatically for any width and height you enter.

How do I scale an image to a new size without distortion?

To scale while keeping the aspect ratio, fix one dimension and calculate the other using the ratio. If your original image is 1920x1080 (16:9) and you want a width of 1280, multiply: height = 1280 x (1080 / 1920) = 720. This calculator lets you enter a target width or target height and it computes the missing dimension for you.

What are the most common image aspect ratios?

The most common aspect ratios are: 16:9 (widescreen video, most modern monitors and TVs, YouTube), 4:3 (older monitors, standard definition TV, iPad), 1:1 (square, Instagram posts), 3:2 (35mm film, most DSLR cameras, standard prints), 2:1 (wide format, some smartphones in panorama mode), and 21:9 (ultrawide monitors). Print sizes like A4 use an irrational ratio close to 1:1.414.

Image Ratio Calculator

Enter the width and height of your image to find the exact aspect ratio in simplest form. Scale to any new width or height while keeping the correct proportions. Works for photos, video, social media, print, and web design.

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Standard formula Aspect ratio reduced using the Euclidean greatest common divisor algorithm.

1. Original Image Size

Width (pixels or any unit)

Height (pixels or any unit)

Or choose a common preset

2. Scale to New Size

Lock dimension for scaling

Target width

Target height

Aspect Ratio Results

Aspect Ratio
16:9
Simplest whole-number form

Decimal Ratio

1.778

Width divided by height

Scaled Width

1280

At target size

Scaled Height

720

At target size

Ratio Breakdown

Original width1920 px

Original height1080 px

Greatest common divisor120

Ratio width component16

Ratio height component9

Aspect ratio16:9

Scaled Dimensions

Scale modeFix width

Target dimension1280 px wide

Scale factor0.667x

Scaled width1280 px

Scaled height720 px

Scaled size1280 x 720

Common Aspect Ratios

Ratio	Decimal	Common use	Example size	Match?

Result: Enter your image dimensions above.

How the Image Ratio Calculator Works

The aspect ratio of an image is the proportional relationship between its width and its height. It is expressed as two numbers separated by a colon, such as 16:9. The numbers represent how many units wide the image is for every unit of height. To find the simplest form, both numbers are divided by their greatest common divisor (GCD).

The Formula

Given a width W and height H:

Find the greatest common divisor: GCD(W, H) using the Euclidean algorithm
Ratio width component = W / GCD(W, H)
Ratio height component = H / GCD(W, H)
The aspect ratio is written as (W/GCD):(H/GCD)

To scale while keeping the same ratio, fix one dimension (for example, a new width W2) and calculate the other: H2 = W2 x (H / W). Alternatively, fix H2 and calculate W2 = H2 x (W / H).

Worked Example

Original image: 1920 x 1080 pixels. Target width: 1280 pixels.

GCD(1920, 1080): 1920 = 1 x 1080 + 840; 1080 = 1 x 840 + 240; 840 = 3 x 240 + 120; 240 = 2 x 120 + 0. GCD = 120.
Ratio = (1920/120):(1080/120) = 16:9
Decimal = 1920/1080 = 1.778
Scaled height = 1280 x (1080 / 1920) = 1280 x 0.5625 = 720 px
Scaled size: 1280 x 720 pixels

These match the default inputs in the calculator above.

Common Aspect Ratios Explained

Ratio	Typical use	Example pixel sizes
16:9	Widescreen video, modern monitors, YouTube, TV	1920x1080, 1280x720, 3840x2160
4:3	Older monitors, standard definition TV, iPad	1024x768, 800x600, 1400x1050
1:1	Square, Instagram posts, profile pictures	1080x1080, 600x600
3:2	35mm film, DSLR cameras, standard photo prints	2736x1824, 6000x4000
4:5	Portrait Instagram posts	1080x1350
9:16	Vertical video, Reels, TikTok, Stories	1080x1920
21:9	Ultrawide monitors, cinema	2560x1080, 3440x1440

Why Aspect Ratio Matters

If you resize an image without maintaining the original aspect ratio, the image will appear stretched or squashed. This is especially important when uploading photos to social media platforms, which often crop or resize images automatically. Knowing the correct ratio lets you crop to the required shape without distortion.

For web designers and developers, understanding aspect ratios helps maintain proportional layouts across different screen sizes. For photographers, the ratio determines how an image will look when printed at standard sizes such as 4x6 inches (3:2) or 5x7 inches (5:7).

Related Calculators

Maths and Stats Calculators: all maths tools in one place.
Aspect Ratio Calculator: general aspect ratio tool for screens and displays.
Area of a Circle Calculator: calculate area from radius or diameter.
Percentage Calculator: find percentages, changes, and portions.

Method: Aspect ratio reduced to simplest form using the Euclidean algorithm for the greatest common divisor (GCD). Scaled dimensions calculated by fixing one side and multiplying the other by the ratio of original dimensions. Standard ratios sourced from common industry conventions for video, photography, and web design.

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