Compress Images Online for Free
Reduce image file sizes with the quality slider and real-time preview. Choose your output format and download instantly. All processing happens in your browser — your images stay private.
How to Compress an Image
Reducing your image file size with ImageSizr.com is straightforward:
- Upload your image — drag and drop, click browse, paste from clipboard (Ctrl/Cmd+V), import from a URL, or connect Google Drive, Dropbox, or OneDrive.
- Adjust the quality slider — the default is 80%, which works well for most images. Move it lower for smaller files or higher for better visual fidelity.
- Review the preview — use the before/after split-view to compare quality, and check the resulting file size.
- Download — click Download to save the compressed image.
Use the Calculate Sizes button to preview file sizes at different quality levels before committing to a setting.
Quality Control Features
ImageSizr gives you precise control over compression:
- Quality slider from 0–100% with preset quick-select buttons at 100%, 75%, 50%, and 25%.
- Real-time file size calculation shows the exact output size before downloading — no guessing required.
- Before/after split-view preview lets you visually compare the original and compressed versions side by side.
Compression only changes the file size through encoding quality. Your image’s pixel dimensions stay exactly the same.
Choosing the Right Output Format
The output format makes a big difference in the final file size and quality:
- JPEG — best for photos and web images. Produces the smallest file sizes but does not support transparency.
- PNG — lossless compression that preserves transparency. Files are larger but quality is pixel-perfect.
- WebP — excellent compression with transparency support. The best choice for modern web optimization.
Learn more about format differences in our guide: JPG vs PNG vs WebP — when to use each.
For format-specific compression, try Compress PNG, Compress JPG, or Compress WebP.
Related Tools
- Resize your images — change pixel dimensions before or after compression for even smaller files.
- Crop tool — remove unnecessary areas to reduce pixel count before compressing.
- Resize to WebP — combine resizing with WebP’s superior compression for optimal web performance.
Explore our image optimization guides for more tips.
Learn More
Frequently Asked Questions
How to compress an image?
1. Upload your image. 2. Adjust the Quality slider (default 80%) or pick a preset (100%, 75%, 50%, 25%). 3. Review the before/after preview and resulting file size. 4. Click Download to save the compressed image.
How much can I reduce the file size?
It depends on the source image and chosen quality. Use the Calculate Sizes button to preview file sizes at different quality levels before downloading.
Does compression reduce the image dimensions?
No. Compression only changes the file size by adjusting encoding quality. The pixel dimensions stay the same.
What happens to transparency when I compress?
If you export as JPEG, transparency is replaced with a background colour (white by default, or your chosen colour). PNG and WebP preserve transparency.
How do I choose the right quality level?
Start at 80% for a good balance of quality and size. Use the before/after split-view preview to compare results visually before downloading.
Is ImageSizr free to use?
Yes. ImageSizr is completely free with no account or sign-up required.
Are my images uploaded to a server?
No. All processing happens directly in your browser. Your images never leave your device, so your data stays private.
What image formats are supported?
You can upload PNG, JPG/JPEG, WebP, GIF, BMP, TIFF, AVIF, SVG, ICO, and HEIC files. Output formats include the original format, JPEG, PNG, and WebP.
How do I upload an image?
You can drag and drop files into the upload area, click Browse to pick a file, paste from the clipboard (Ctrl/Cmd+V), import from a URL, or connect Google Drive, Dropbox, or OneDrive.