This calculator works out the exact aspect ratio of an image, screen, video or print size from its width and height, then shows you how to resize it without stretching or squashing it. Enter your original width and height in any unit, or pick a preset such as Full HD, 4K, a square Instagram post or A4 at 300 dpi, and the tool reduces the two numbers to their simplest whole-number ratio using the greatest common divisor, plus the equivalent decimal ratio. Choose whether to lock the width or the height, enter your target size, and it calculates the missing dimension so the proportions match the original exactly. The results show your simplest aspect ratio, the decimal ratio, and the scaled width and height, backed by a breakdown of the GCD calculation and the scale factor used. A comparison table then checks your ratio against ten common standards, including 16:9, 4:3, 1:1, 3:2 and 9:16, flagging an exact match and naming its typical use, from widescreen video and DSLR photos to Instagram Stories and ultrawide monitors. Use it before resizing photos for social media, planning a video project, laying out a print job, or building a responsive web layout, so you know whether your new size will distort the image and what the correctly proportioned dimensions should be instead.
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Standard formula
Aspect ratio reduced using the Euclidean greatest common divisor algorithm.
1. Original Image Size
px
px
2. Scale to New Size
px
px
Aspect Ratio Results
Aspect Ratio
16:9
Simplest whole-number form
Decimal Ratio
1.778
Width divided by height
Scaled Width
1,280
At target size
Scaled Height
720
At target size
Ratio Breakdown
Original width1,920 px
Original height1,080 px
Greatest common divisor120
Ratio width component16
Ratio height component9
Aspect ratio16:9
Scaled Dimensions
Scale modeFix width
Target dimension1,280 px wide
Scale factor0.6667x
Scaled width1,280 px
Scaled height720 px
Scaled size1,280 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).
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.
