How do I keep an image in proportion when resizing?

Lock the aspect ratio and change only one dimension. Enter your target width and the calculator gives the height that preserves the ratio (or vice versa), so nothing gets stretched.

What does the simplified ratio mean?

It reduces your width and height to the smallest whole-number ratio using the greatest common divisor — for example 1920×1080 simplifies to 16:9.

Which ratios are common for social and video?

16:9 for landscape video/YouTube, 9:16 for Stories/Reels/TikTok/Shorts, 4:5 for Instagram portrait posts, and 1:1 for square posts.

Aspect Ratio Calculator

Work out the missing width or height for any aspect ratio. Pick a preset (16:9, 9:16, 4:5, 1:1, and more) or type a custom ratio, then enter the width or height you’re exporting at — the other dimension is filled in instantly so your image or video keeps its proportions. It also shows the decimal ratio and the simplified W:H.

How to use Aspect Ratio Calculator

Choose an aspect ratio preset or type a custom W:H.
Enter the width OR the height you want.
Read the matching dimension, plus the decimal and simplified ratio.

Frequently asked questions

How do I keep an image in proportion when resizing?: Lock the aspect ratio and change only one dimension. Enter your target width and the calculator gives the height that preserves the ratio (or vice versa), so nothing gets stretched.
What does the simplified ratio mean?: It reduces your width and height to the smallest whole-number ratio using the greatest common divisor — for example 1920×1080 simplifies to 16:9.
Which ratios are common for social and video?: 16:9 for landscape video/YouTube, 9:16 for Stories/Reels/TikTok/Shorts, 4:5 for Instagram portrait posts, and 1:1 for square posts.

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