Keep pixels square unless you know otherwise
This calculator assumes square pixels, which is correct for most web images, modern video exports and design tools. Some broadcast and archival formats use non-square pixel aspect ratios and need separate handling.
Example
A 1920 by 1080 image reduces to a 16:9 aspect ratio. If the target width is 1280, the matching height is 1280 x 1080 / 1920 = 720.
Common mistakes
Do not resize width and height independently unless you intend to distort the image. Preserve the ratio when preparing thumbnails, video exports or responsive images.
Limitations
The calculator does not crop, pad, upscale intelligently or account for non-square pixels. It only computes proportional dimensions.
Last reviewed: 2026-05-17