Resize an image

Set the dimensions you actually need — a 1200px-wide hero, a 512px avatar, a photo that finally fits an upload box. slimdocs scales with a high-quality filter, keeps the aspect ratio unless you ask it not to, and never enlarges a picture behind your back.

How to use it

1. Open the Resize Image tool and drop in your photo.
2. Enter a width, a height, or both — leave one blank to scale proportionally.
3. Choose whether to keep the aspect ratio or fill and crop the box.
4. Resize, then download the result.

Width, height, or both

Filling in just one dimension is usually what you want. Give a width of 1200 and leave the height blank, and the image scales proportionally — the result is 1200 pixels wide at whatever height preserves the original shape. That is the safe default, because it can never distort anything.

Filling in both dimensions asks for a specific box, and then the fit setting decides what happens when your image is a different shape from that box. "Keep aspect ratio" scales the photo until it fits entirely inside the box, so the final size may be smaller than what you asked for in one direction. "Fill and crop" scales until the box is completely covered and trims the overflow — the result is exactly the dimensions you asked for, at the cost of losing a strip from the edges.

Why enlarging is off by default

A digital photo only contains the detail that was captured when it was taken. Asking for a bigger version does not recover detail that was never there — the software has to invent the extra pixels by interpolating between the ones it has, and the result looks soft and slightly plastic.

Because of that, slimdocs will not make an image larger than its original unless you explicitly tick the enlarging option. If you ask for a 3000px width on a 900px photo and leave that box unticked, you get the original 900px image back rather than a blurry upscale you would have thrown away anyway.

Common sizes worth knowing

Most resizing requests come from a handful of familiar constraints:

1920 × 1080	Full-HD screen background, or a presentation slide that fills the display.
1200 wide	A comfortable maximum for a blog or article image — sharp on retina screens without being wasteful.
800 wide	Body images inside a document or email newsletter.
512 × 512	Square avatars, app icons and profile pictures on most platforms.
150 wide	Thumbnails and list previews, where file size matters far more than detail.

Resizing and file size

Halving both dimensions of an image removes roughly three-quarters of its pixels, which usually cuts the file size by a similar order. That makes resizing the single most effective thing you can do when a photo is too large for an upload limit — far more effective than turning the compression up on an image that is still 6000 pixels wide.

If the file is still bigger than you need after resizing, run it through the compressor afterwards, or convert it to WebP. The two steps compound: a resized, WebP-encoded photo is routinely a twentieth of the original.

Orientation and quality are preserved

Photos from phones and cameras store their orientation as a separate EXIF tag rather than by actually rotating the pixels, which is why an image sometimes appears sideways in one program and upright in another. slimdocs reads that tag and bakes the correct orientation into the output, so your resized photo is the right way up everywhere.

The image is processed in memory and deleted as soon as your download starts. Nothing is written to disk, and the original is never retained.