Image Resizer with Locked Aspect Ratio

What does an image resizer do?

Resizing scales an image to new pixel dimensions by drawing it onto a canvas at the target width and height, using the browser's built-in interpolation to fill in or discard pixels as needed. Unlike cropping, nothing is cut off — the entire original image is retained, just stretched, shrunk, or squashed to fit the new dimensions.

The Lock ratio option constrains width and height to the source image's original aspect ratio, so typing a new width automatically recalculates a proportional height (and vice versa). Turning it off lets you set width and height independently, which is useful when you need an exact size but accept some distortion — though for most use cases you'll want the ratio locked to avoid stretched-looking output.

When to use it

Use it to shrink oversized photos before uploading them somewhere with a file-size limit, generate a specific pixel size required by a spec (app store icons, ad banners, social media dimensions), or scale down a screenshot so it fits inline in documentation without needing CSS to constrain it. Downscaling large images is also a straightforward way to cut file size significantly, since fewer pixels means less data to encode regardless of format.

If you need to both resize and change the file format (say, PNG to WebP), resize first — the format converter re-encodes whatever pixels you feed it, so getting the dimensions right beforehand avoids doing a second lossy pass.

Example

Upload a 4000×3000 camera photo — the tool detects its dimensions and pre-fills them. Set width to 1200 with Lock ratio on, and height auto-updates to 900, preserving the 4:3 aspect. Click Resize and the output renders at exactly 1200×900, downloaded as resized-1200x900.png — a fraction of the original file size with no visible quality loss at typical web display sizes.