What this calculator does
Enter the original dimensions, choose which target side you know, and the missing side is calculated automatically. This prevents the distortion caused by changing width and height independently.
Resolution formulas
Target height = target width × original height ÷ original widthTarget width = target height × original width ÷ original heightWorked examples
1920 × 1080 resized to 1280 wide
The matching height is 720 pixels, preserving the original 16:9 ratio.
4000 × 3000 resized to 1200 high
The matching width is 1600 pixels, preserving the original 4:3 ratio.
Frequently asked questions
Does this tool resize my image file?
No. It calculates the dimensions to use in an image editor, CMS, or design tool.
Why is the result rounded?
Pixel dimensions must be whole numbers, so the proportional result is rounded to the nearest pixel.
Will the aspect ratio always be exact after rounding?
For some dimensions the nearest whole pixel introduces a tiny difference. It is generally too small to see.
What happens if I upscale a small image?
The dimensions will be correct, but calculating larger numbers does not create real detail. Upscaling quality depends on your resampling method.