Image Resizer: Exact Dimensions, No Upload

Resizing and compressing are two different jobs

People use the words interchangeably, and that is why the fix so often fails. An image has two independent properties. Its dimensions are how many pixels wide and tall it is — 4000 × 3000, say. Its file size is how many bytes it takes to store that grid, which depends on the format and how aggressively it was encoded. You can change either one without touching the other.

They overlap in one direction only: resizing down almost always shrinks the file as a side effect, because you deleted most of the pixels. Dropping 4000 × 3000 to 1200 × 900 removes about 91% of them. So if a photo is both too big on screen and too heavy, resize first and check whether the file is already small enough before compressing at all. If the dimensions are correct and only the weight is wrong, this is the wrong tool — use the Image Compressor instead.

Down is safe. Up cannot invent detail.

Shrinking an image is a question of which real pixels to keep and how to blend the rest. Enlarging is a question of what to make up. That asymmetry is arithmetic, not a limitation of any particular program. A 400 × 400 image contains 160,000 pixels; a 1200 × 1200 version needs 1,440,000. Eight of every nine pixels in that result have to be guessed by averaging neighbours, and averaging is exactly the thing that produces soft edges and mushy text.

So when you ask this tool for dimensions larger than the original, it shows an amber warning with the exact factor rather than pretending. It will still do it — sometimes you genuinely need a small logo to fill a required box — but you should know what you are getting before you download it, not after a client points at it. The honest fix is upstream: find the largest original you have and resize down from that.

Downscaling has its own trap, which the tool handles for you. One enormous jump aliases badly. If a browser shrinks a 4000-pixel photo straight to 200 pixels in a single draw, each output pixel is sampled from only a handful of the twenty source pixels it should represent, and the rest are thrown away untouched. The result is jagged diagonals, shimmering fine textures, and text that breaks up. This tool avoids it by successive halving: whenever the reduction is more than about 2×, the image is shrunk by half repeatedly until it is within 2× of the target, then drawn once at the exact size. Each halving averages every source pixel into the result, so nothing gets skipped. The panel beside the preview tells you how many halving steps your particular image needed.

Dimensions people actually ask for

These are the sizes behind the preset buttons in the tool. Read them as common conventions, not official specifications: every platform in this table changes its crops and display sizes from time to time and almost none of them announce it. If a pixel-perfect result genuinely matters — a paid ad, a print job — check the platform’s own help pages on the day.

“Yours” in the ratio column means the width-only presets keep your original aspect ratio and calculate the height for you — nothing is cropped. Note that this table is about dimensions. If you also need to hit a file-size limit in kilobytes, that is the compressor’s job, and our guide on getting an image under 100 KB walks through it.

What “crop to fill” and “stretch” do to a face

Aspect ratio is just width divided by height. A 3:2 photo from a camera does not fit a 1:1 Instagram square or a 4:1 LinkedIn banner, and something has to give. The tool gives you three honest answers and no dishonest ones.

• Lock the aspect ratio (on by default). You type a width, the height is calculated. The shape never changes and nothing is ever cropped or distorted. This is the right choice for the large majority of resizes.
• Crop to fill — available once you unlock the ratio and type both numbers. The image is scaled until it covers the target box, and the overflow is trimmed evenly from the centre. Every shape in the frame stays correct; you simply see less of the edges. A face keeps its proportions and may lose some hair or shoulder.
• Stretch to fit — the whole image is squashed into the new shape. Nothing is lost from the edges and everything is wrong: a face forced from 3:2 into 1:1 becomes about 33% too wide, straight lines lean, and circles turn into ovals. Almost nobody wants this, but it exists because occasionally you are resizing a texture or a gradient where distortion is harmless.

There is a fourth option hiding in the Fit within a box mode: give a maximum width and height and the image is scaled down until it fits entirely inside them, keeping its ratio. One side usually ends up smaller than the box and nothing is cropped at all. That is the safest mode for bulk-feeling work like “get every photo under 1200 px in either direction,” because you never have to think about which images are landscape and which are portrait. One caveat on cropping: the crop is always from the geometric centre. There is no face detection and no draggable crop box, so if your subject sits near an edge, check the preview before you download — you may need to crop the photo yourself first and then resize it here.

Which format to save the resized copy as

Resizing re-encodes the image, so you get to reconsider the format for free. The tool offers three, plus “keep original.”

Three honest footnotes. (1) The quality slider is greyed out for PNG on purpose. PNG stores every pixel exactly, so a quality setting has nothing to act on — a lot of tools leave the control enabled anyway, which is just theatre. (2) Choosing JPEG for a transparent PNG fills the transparent areas with white before encoding, because JPEG has no alpha channel at all; the tool says so on screen when it applies. (3) “Keep original” can only really keep JPEG, PNG, or WebP — those are the formats a browser canvas can write. A GIF, BMP, or AVIF source will be decoded and saved as PNG, and animated GIFs come out as a single still frame. If you want the format trade-offs in more depth, our comparison of JPEG vs PNG vs WebP vs AVIF covers AVIF too.

Where your image goes, and what this tool will not do

It goes nowhere. Your browser reads the file you chose, decodes it, draws it onto a <canvas> at the new size, and re-encodes it — all on your own machine. There is no upload, no server that has ever seen the picture, no account, and no storage. Closing the tab discards both the original and the result. That matters more than it sounds for scanned documents, ID photos, screenshots with customer data in them, and family pictures, all of which people paste into random web tools every day. It also means the file size shown next to the preview is the real encoded output rather than an estimate: the image already exists in your browser and the download button just saves it.

The honest limits that come with that design: one image at a time — there is no batch queue, because the right size is usually a per-image judgement; dimensions are capped at 12,000 px per side; very large photos are limited by your own device memory, so a 100-megapixel file may be slow on an older phone; EXIF metadata is not carried across — the re-encoded copy has no camera settings, date, or GPS location, which is a privacy win but worth knowing if you rely on that data; and the tool deliberately does not try to hit a target file size in kilobytes. That is the Image Compressor’s job. If you would like the whole workflow written out, see how to resize an image.

Frequently asked questions