Image Resizer

Resizing is the least glamorous and most impactful thing you can do to an image. Before any clever compression, matching the pixel dimensions to the actual display size removes the bulk of wasted bytes — and it is the step most people skip because their camera or screenshot tool produces whatever size it feels like. This is exactly the job an image resizer does best: type the dimensions, choose how the box is filled, download the result. An online image resizer that works in exact pixels or percentages, keeps the aspect ratio unless told otherwise, and never uploads a thing — that is the whole tool.

Pixel dimensions, DPI and why DPI does not matter here

A common source of confusion: a "300 DPI" image and a "72 DPI" image with the same pixel dimensions contain exactly the same amount of data. DPI is a print instruction that tells a printer how densely to place those pixels on paper. For screens, only the pixel count matters. This image resizer works in pixels, which is what every web, app and social platform actually consumes.

If you are preparing for print, work out the physical size you need and multiply by the target DPI: an A4 page at 300 DPI is roughly 2480 × 3508 pixels — type that into the image resizer and the print box is covered.

How to resize an image: the three ways a box gets filled

There are no presets in the image resizer — you type the numbers. What actually decides the outcome is how the image is allowed to meet them, and that is one dropdown with three honest answers.

• Fit inside scales until the whole image sits within the box, then stops. A 4000 × 3000 photo aimed at a 1000 × 1000 box comes out 1000 × 750: inside the box, correct proportions, not square. This is the right default when you resize images for the web, where the number you care about is a maximum width.
• Fill and crop scales until the image covers the box, then trims the overflow evenly from both sides. The same photo comes out exactly 1000 × 1000, with a strip removed from the left and the right. Use it for avatars, thumbnails and any grid where every tile has to be the same shape.
• Stretch honours both numbers exactly and ignores the ratio entirely. It is the only mode that can distort a face, and it can never happen by accident.

Leave a field empty and there is nothing to negotiate: enter a width of 1200 and the height follows the original ratio whichever mode is selected. That is the everyday case for an image resizer — one number in, correct proportions out.

Common sizes to resize images to

These are the numbers people type into an image resizer most often:

• 1080 × 1080 — Instagram feed, LinkedIn posts, square product tiles.
• 1080 × 1920 — stories, reels and any vertical full-screen format.
• 400 × 400 — avatars; platforms downscale these hard, so 400 is plenty.
• 600 wide — email, where clients cap the layout at around 600 CSS pixels.
• 1920 × 1080 and 3840 × 2160 — video thumbnails and full-screen backgrounds.

When distortion is the right answer

Almost never. Faces and product proportions are the first things to look wrong, and a stretched logo reads as carelessness rather than as a decision. A good image resizer makes distortion impossible by accident, and this one does: Stretch is the only mode that can distort, and it must be chosen deliberately. Stay on Fit inside or Fill and crop and the proportions look after themselves.

Stretch earns its place in three narrow cases: a texture or gradient with no recognisable subject, a background element being pulled to an awkward container, and a file that has to be exact dimensions for a validator which checks the numbers and nothing else. If you are reaching for it because an image must fill a fixed area on a page, the better answer lives in CSS — object-fit: cover crops in the browser and leaves the original file usable at every other size.

Upscaling honestly

Browsers upscale by interpolation: they estimate new pixel values from their neighbours. The result is smooth but soft, and no amount of sharpening restores detail that was never captured. Any image resizer can enlarge an image; this one is honest about what enlarging costs. If you must enlarge, do it in modest steps (no more than 150–200% at a time) and expect a painterly result rather than a crisp one.

In exact-size mode the tool takes your side by default: ask for a box larger than the original and the request is quietly scaled back to the source, so one ambitious number cannot inflate a whole batch. Tick Allow enlarging when you genuinely want it and the size is honoured as typed. Percentage mode makes no such judgement — it is a direct multiplier, so 200% doubles both edges whether that is wise or not.

Quality, format and what the numbers mean

Percentages compound, which is why they cut weight faster than people expect. Halving both edges quarters the pixel count, so 50% is closer to a 75% saving than a 50% one, and 25% leaves you with a sixteenth of the pixels you started with. The same arithmetic is the trap going the other way: 200% asks the encoder to invent three pixels for every one it was handed.

The quality slider runs from 40 to 100 and starts at 92, which is deliberately generous — a freshly resized image has already given up detail and there is no reason to compound that with a hard encode. The image resizer hands the redrawn bitmap to the browser's own encoder, which is why the slider behaves the same here as it does in the converters. It disappears when you choose PNG, because PNG is lossless and the setting would do nothing. Leave the format on Same as input to keep whatever you brought, or choose PNG or WebP to protect transparency; JPG will flatten it onto white.

What you get back from the image resizer

The image resizer renames every file with its finished dimensions, so portrait.jpg resized to 800 × 1200 arrives as portrait-800x1200.jpg and no original is overwritten. Each row reports the whole journey — the source dimensions, the new dimensions, and the file size before and after — which is what makes an image resizer trustworthy at scale: you never take the numbers on faith.

Batch image resizing, privately

The image resizer processes twenty images per run, 25 MB each, decoded, redrawn and re-encoded in this tab. Nothing is uploaded, nothing is queued, and no account is asked for — the same rules every tool on CollabsTool follows. Whether you resize images once a month for a newsletter or run a twenty-file batch through the image resizer every morning, the work happens on your machine and the originals stay untouched. For most people who need to resize image files regularly, that combination — exact pixels, honest reporting, zero upload — is the whole reason to do it in the browser rather than in a desktop editor or an upload-based service.