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Aspect Ratio Missing Dimension Calculator
Know the width but not the height—or the height but not the width? Enter an aspect ratio and one dimension to calculate the other while preserving proportions.
Set the ratio and known dimension
Calculated dimensions
Height = width × ratio height ÷ ratio width
Formula
If width is known: height = width × ratio height ÷ ratio width.
If height is known: width = height × ratio width ÷ ratio height.
Example: a 1920-pixel-wide frame at 16:9 has a height of 1920 × 9 ÷ 16 = 1080 pixels. Fractional answers are shown to two decimal places; round to whole pixels when required by your workflow.
Common aspect ratios
16:9 is widely used for widescreen video, 9:16 for vertical video, 1:1 for square layouts, and 4:5 for portrait social posts. Select the ratio that matches your intended canvas or platform specification.
This calculator preserves proportions mathematically. It does not resize or export an image file. Use the Image Resize Calculator if you need to create a resized image.
Frequently asked questions
Can I use a custom ratio?
Yes. Enter any positive ratio width and height, such as 3 and 2 for 3:2.
Why is my result fractional?
Some input dimensions do not produce a whole-number missing side. The exact proportional result is displayed to two decimal places; you may need to round for pixel-based output.
Related tools: Ratio Simplifier · CSS Aspect-Ratio Generator · 16:9 Size Guide.