Aspect ratio calculator
Find a simplified width-to-height ratio and calculate a matching dimension for a new size.
Simplified ratio of the original dimensions.
Your inputs stay in this browser. Nothing is uploaded or saved in an account.
Two numbers describe the shape.
Aspect ratio compares width with height. Divide both dimensions by their greatest common divisor to simplify it: 1,920 × 1,080 becomes 16:9. The ratio describes shape, not image quality or file size.
New width = new height × original width ÷ original height
A 1,920 × 1,080 image resized to 1,280 pixels wide becomes 720 pixels high. At a width that produces a fractional height, this tool rounds to the nearest whole pixel, with a minimum of one pixel. The resulting shape can therefore differ very slightly.
Resizing and cropping solve different problems.
Matching a ratio preserves the full image when it is resized proportionally. Filling a box with a different ratio requires cropping, padding or distortion. This calculator does not edit or crop a file, and the preview is a diagram rather than a print-size representation.
Pixels and print inches are different quantities. Do not infer print sharpness from the ratio alone. Keep important text and faces away from edges if the final publishing platform may crop the image.
Resize an actual image locally · Read about dimensions, compression and print resolution.
A few useful answers
Does 16:9 mean HD?
No. Both 640 × 360 and 3,840 × 2,160 have a 16:9 shape. Their pixel counts and possible detail differ.
Why is a calculated dimension rounded?
Raster images use whole pixels. A target dimension may not produce an exact integer match, so the nearest pixel is shown.
Will it stretch my image?
This page does not edit a file. Its matching dimension preserves the original shape as closely as whole pixels allow.