Documents, reports and covers printed anywhere outside North America
Posters and flyers at a standard, cheap size
Certificates, in landscape
Anything that may later be scaled to A5 or A3
Resizing to A4
The √2 ratio, and what it buys you
Every ISO 216 size shares one proportion: the long side is the square root of two times the short side. That is what makes A4 fold in half to exactly A5, and two A4 sheets side by side exactly A3, with no change of shape.
In practice it means a design made at A4 scales to any other A-size without reflowing or re-cropping. Print the same artwork at A5 for a handout or A3 for a poster and the layout is unchanged; only the physical dimensions move. No North American size has this property, which is why converting between A4 and Letter is fiddly and converting between A4 and A3 is not.
Why 2480 × 3508
210 millimetres is 8.268 inches, and at 300 dots per inch that is 2480 pixels. 297 millimetres is 11.693 inches, which is 3508.
For a full-bleed design — colour running to the edge — add 3 millimetres on every side, which at 300 DPI makes the working canvas 2516 × 3544 for a page that trims to 2480 × 3508. Nothing you want to see should live in that outer band; all of it is going in the bin.
Pull the other way too: keep text and logos at least 5 millimetres inside the trim, and 10 if the document will be bound.
The office printer margin nobody plans for
Most A4 documents are printed on an office printer rather than at a print shop, and office printers cannot print to the edge. They enforce an unprintable margin of typically 4 to 5 millimetres and their driver silently scales the page down to fit it.
A full-bleed cover printed that way comes out with a white border and every element slightly smaller than designed. If the page will realistically be printed in an office, design it with a white margin from the start and the result matches the intent.
Yes. Resizing JPG, PNG, and WebP images is completely free with no sign-up, no watermark, and no file limit. Resizing runs entirely in your browser, so there is nothing for us to charge for. Pro plans add the AI tools, but everyday resizing stays free forever.
Are my images uploaded to a server?
No. OpusImg resizes images on your own device using WebAssembly and your browser's own canvas. Your files never leave your computer or phone — there is no upload, no cloud processing, and nothing stored on our side. That makes it safe for confidential documents, client work, and personal photos.
How do I resize an image to exact pixel dimensions?
Choose the "By dimensions" mode and type the width and height you need in pixels. Leave the aspect-ratio lock on to keep the image's proportions — change one field and the other follows automatically. Turn the lock off when you need an exact, possibly non-proportional canvas, such as a specific banner size.
What is the lock aspect ratio toggle for?
When the lock is on, the width and height stay proportional: setting the width to 1000px updates the height to match the original shape, so the picture is never squashed or stretched. When the lock is off, you can set width and height independently, which is useful for fitting an exact canvas even if it distorts the image slightly.
Which resampling algorithm should I pick?
Use Lanczos for photographs — it produces the sharpest, most natural result and is the default. Bicubic is a fast, smooth alternative handled by your browser. Choose Nearest neighbour only for pixel art, sprites, or icons where you want hard edges and no blending between pixels when scaling up.
What does the DPI setting do?
DPI (dots per inch) is metadata that tells print software how large to print the image. It does not change the pixel dimensions or how the image looks on screen — 72 DPI is standard for the web, while print shops usually want 150 or 300 DPI. We embed the value you choose into the file (PNG and JPG) so a print workflow reads the right density.
Can I resize for Instagram, YouTube, or other platforms?
Yes. The "By preset" mode includes 18 ready-made sizes — Instagram square, portrait, and story; Facebook and LinkedIn covers; X/Twitter headers; YouTube thumbnails and channel art; Pinterest pins; plus HD, QHD, and 4K. Pick a preset and your image is resized to the exact canvas that platform expects.
Will resizing reduce image quality?
Making an image smaller (downscaling) keeps it looking crisp — Lanczos and bicubic both average pixels cleanly. Making it larger (upscaling) can only invent so much detail, so very large enlargements look soft; for big upscales the AI upscaler in Pro reconstructs detail far better. We encode the result at high quality so the resize itself adds no visible compression artifacts.
Can I resize many images at once?
Yes. Drop a whole folder and apply one target to the batch. In percentage mode every image is scaled by the same percentage, so each keeps its own aspect ratio; in dimensions or preset mode every image is fitted to the same canvas. Results are bundled into a single ZIP for download, all processed on-device.
What formats can I resize?
You can drop in JPG, PNG, WebP, AVIF, GIF, BMP, TIFF, and HEIC. Each file is decoded in your browser, resized, and re-saved — JPG and HEIC come out as JPG, PNG/BMP/TIFF as PNG, and WebP/AVIF/GIF as WebP, so the result always opens everywhere. To change format deliberately, use the converter tool linked below.