Compress ZIP Files Online
Re-compress ZIP archives with maximum DEFLATE compression for smaller file sizes. Perfect for sharing and storage.
Drop a ZIP file here or click to browse
Re-compress for smaller file size
Re-compress ZIP files with maximum DEFLATE compression
Three compression levels to choose from
Smart handling of already-compressed formats (High mode)
100% client-side — files never leave your device
No file size limits for compression
No watermarks, no sign-up required
ZIP Files That Compress Well
ZIP re-compression helps most when the original archive was made quickly or with default settings. Text, CSV, code, and office documents usually shrink the most because the ZIP layer can find repeated patterns. Photo, music, and video folders may not change much because those formats are already compressed.
Privacy and Troubleshooting
The archive is unpacked and rebuilt in your browser, so private project folders and client handoff files do not need to be uploaded. If the result is larger, try High mode for mixed folders or keep the original ZIP if it already uses maximum compression.
Frequently Asked Questions
How does ZIP re-compression work?
Many ZIP files are created with default or low compression settings. Compresso reads your ZIP, extracts all files, and re-compresses them using maximum DEFLATE compression for smaller output.
What's the difference between compression levels?
Low uses DEFLATE level 6 for faster processing. Medium uses level 9 for better compression. High uses level 9 and intelligently stores already-compressed formats (JPG, PNG, MP3, MP4, etc.) without re-compressing them, since they don't benefit from DEFLATE.
Will re-compression damage my files?
No. Re-compression is lossless — your files inside the ZIP remain bit-for-bit identical. Only the ZIP compression layer changes.
How much smaller will my ZIP get?
Results vary based on original compression settings and file types. ZIP files created with low compression or containing text, documents, or uncompressed data can see 10–40% reduction. Files already compressed at maximum will see minimal change.
Is it safe to compress ZIP files with Compresso?
Absolutely. Compresso processes everything in your browser — your files are never uploaded to any server. Your archives stay completely private on your device.
What file types benefit most from re-compression?
Text files, documents, spreadsheets, source code, and XML-based formats see the biggest improvements. Already-compressed media (JPG, PNG, MP4) won't shrink further.