No upload, 100% local, no account

Resize images

Resize your images locally: no upload, no privacy concerns. Supports JPEG, PNG, WebP and AVIF.

How Resize images works

Image Resize runs entirely inside your browser using the @jsquash/resize WebAssembly module with Lanczos-3 filtering. You drop a JPEG, PNG, WebP or AVIF file, enter target dimensions or a percentage scale, and the resampled image is offered as a local download within seconds. The pixel data never leaves your device: no server receives your file, no account is required, and once the WebAssembly module has been fetched (a one-time download the first time you resize an image), the tool keeps working with no network connection.

Lanczos-3 is a high-quality downscaling kernel that preserves edge sharpness better than bilinear or nearest-neighbour methods. You can also change format at the same time, converting a heavy PNG screenshot to a compact WebP or AVIF in a single pass. The quality slider (for lossy formats) gives you direct control over the size-versus-fidelity trade-off, and a live size estimate updates as you drag.

Written by Bastien Sulyan

How to use Resize images, step by step

  1. Drop your image onto the upload area or click to browse. Accepted formats: JPEG, PNG, WebP, AVIF.
  2. Enter the target width, height, or a percentage scale. Lock the aspect ratio to avoid distortion.
  3. Select the output format and, for lossy formats, set the quality with the slider.
  4. Click Resize. Processing runs locally in a Web Worker using WebAssembly.
  5. Click Download to save the result to your device.

Common use cases

  • A web developer needs to produce a 800 px wide WebP hero image from a high-resolution raw PNG without uploading the raw file to a third-party service.
  • A social-media manager scales a portrait photo to exactly 1080x1080 px for an Instagram post and converts it to JPEG in one step.
  • A journalist preparing images for a content management system resizes and compresses several photos offline on a laptop without network access.
  • A designer checks how a high-DPI asset looks at half its original dimensions before committing to a final export from the design tool.

Frequently asked questions

Does the resizer send my image to a server at any point?

No. The image is read from your local disk, decoded into an OffscreenCanvas, resampled by the @jsquash/resize WebAssembly module, then re-encoded to the chosen format, all inside this browser tab. Open your browser's Network panel while resizing and you will see no request carrying image data.

Which formats can I read and write?

You can open JPEG, PNG, WebP and AVIF files. Output can be any of those four formats. Choosing a different output format and resizing happen in the same single pass, so there is no need for a separate conversion step.

What resampling algorithm does the tool use?

Lanczos-3, implemented in the @jsquash/resize WebAssembly module. It preserves sharpness at downscaled sizes better than bilinear interpolation and avoids the blocky artefacts of nearest-neighbour. For upscaling, Lanczos is also applied, though upscaling cannot recover lost detail.

Can I resize an image while keeping the original aspect ratio?

Yes. The aspect-ratio lock is on by default. Enter a value in either the width or the height field and the other field updates automatically. Unlock it only if you need to stretch the image to non-proportional dimensions.

Does the tool work if I have no internet connection?

Mostly. The resampling itself always runs on your device, your image never leaves your machine. The one caveat is that the @jsquash/resize WebAssembly module is a sizeable download fetched from this site the first time you resize an image; once that download and the page have both completed, you can disconnect from the network and continue resizing images without interruption.

Why is the output file larger than the original?

Switching to a lossless format like PNG or raising the quality level on a lossy codec can produce a larger output than a heavily compressed original. Lower the quality slider or choose a more efficient format (WebP or AVIF) to bring the size down.

Does the resized image carry a watermark?

No. The output is only the resampled pixel data, with no watermark, logo or Sunasty branding added anywhere.

Can I resize a photo on my phone right after taking it?

Yes. The tool works the same in mobile Chrome or Safari as on desktop, so you can drop a photo straight from your phone's camera roll. The WebAssembly module still needs its one-time first-use download (see the offline answer above), which counts against mobile data if you are not on Wi-Fi.

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