Resize by pixels, keep the shape
Digital images are grids of pixels, and resizing means asking the browser to redraw that grid at a new size. The part people get wrong is the shape. Every image has an aspect ratio, the relationship between its width and height, and if you change one without adjusting the other, faces stretch and circles turn into eggs. That is why the aspect ratio lock is on by default: type a new width and the matching height is worked out for you.
The tool shows the original dimensions as soon as your image loads, so you always know what you are starting from. PNG files stay PNG, which preserves transparency; everything else is saved as JPG.
Worked examples
Downscaling is safe, upscaling is not
Shrinking an image works well because the browser has more information than it needs: it blends neighbouring pixels together using high quality smoothing, and the result looks sharp at its new size. Enlarging is a different story. If the detail was never captured, no resizer can invent it, so an image pushed beyond its original dimensions comes out soft and slightly blurry. If you need something bigger, go back to the source and export it larger; if that is impossible, enlarge as little as you can get away with.
A practical habit: keep your original at full resolution and resize copies down for each use. A photo destined for a web page rarely needs to be wider than 2000 pixels, an email attachment is happier at 1200, and a thumbnail can be 400 or less. Sending a 12 megapixel photo to fill a 300 pixel slot wastes bandwidth and slows the page for no visible benefit. Fewer pixels also means a much smaller file, which is often the real goal; if the file is still too heavy after resizing, run it through the image compressor as a second step.
Nothing is uploaded, ever
Everything on this page happens inside your browser. The image is read from your device, redrawn on an invisible canvas, and offered back as a download, all locally. It is never sent to a server, never logged and never stored, which makes the tool safe for private photos, client work and anything else you would rather not hand to a random website. Close the tab and every trace is gone.
Because the work is done by your own machine, speed depends on your device rather than your connection. Even large photos resize in a fraction of a second on a modern phone or laptop, and you can try as many sizes as you like before downloading, the result updates live as you type.
Frequently asked questions
Is my image uploaded anywhere?
No. The resizing is done by JavaScript running on your own device, using the browser's built-in canvas. The image never travels over the internet, nothing is logged or stored, and closing the tab removes everything.
Will resizing reduce the quality?
Making an image smaller discards pixels, but browsers use high quality smoothing so the result usually looks crisp at its new size. Making an image larger cannot add detail that was never captured, so upscaled images look soft. Resize down whenever you can.
What does the aspect ratio lock do?
It keeps width and height in the same proportion as the original, so nothing looks stretched or squashed. Change one dimension and the other updates automatically. Untick it only if you deliberately want to distort the image.
Does the tool keep my file format?
PNG files are saved as PNG, which keeps any transparency. Other formats, including JPG and WebP, are saved as JPG on a white background. The download name includes the new dimensions so you can tell versions apart.
What size should images be for the web?
For a full width photo on a modern site, 1600 to 2000 pixels wide is usually plenty. Blog images are often about 1200 wide and thumbnails 400 or less. Anything bigger than the space it will occupy is wasted bytes, so resize to roughly the displayed size.