ZIP Split & Reassemble

Split large ZIP archives into smaller parts for email, FAT32, or cloud upload limits, then reassemble them back. Byte-level splitting runs entirely in your browser.

Processed locally

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How to Use

Split large ZIP archives into smaller byte-level parts, or reassemble previously split parts back into the original archive. Everything runs in your browser using the File API — no data leaves your device.

How to split a ZIP file

Select Split mode — this is the default mode when the tool loads. Use the mode toggle at the top to switch between Split and Reassemble.
Drop or select your ZIP file. The tool accepts .zip archives of any size.
Set the part size by entering a value in megabytes or clicking one of the quick presets: 5 MB, 10 MB, 25 MB, 50 MB, 100 MB, or 250 MB. The estimated part count updates in real time.
Click "Split ZIP" to start processing. A progress bar tracks the operation. Splitting uses File.slice() to extract each chunk without loading the entire archive into memory.
Download individual parts using the download button next to each part, or click "Download All as ZIP" to get every part packaged in a single archive.

How to reassemble ZIP parts

Switch to Reassemble mode using the mode toggle at the top.
Add part files by dragging them into the dropzone or clicking to browse. Add as many parts as needed — each drop appends to the list.
Review the order. Parts are auto-sorted by their numeric extension (.001, .002, etc.) during reassembly. You can also reorder manually using the arrow buttons.
Remove unwanted files by clicking the X button next to each part.
Click "Reassemble ZIP" to concatenate all parts into a single archive. The tool reads each file in 1 MB chunks for memory efficiency.
Download the reassembled ZIP. The output filename is derived from the first part, with the numeric suffix stripped and .zip ensured.

About This Tool

How ZIP splitting works at the byte level

ZIP splitting in this tool is a byte-level operation, not an archive-level one. The tool does not parse the ZIP directory structure or extract individual files. Instead, it treats the archive as a raw binary blob and divides it into fixed-size chunks. This approach has two key advantages: it works on arbitrarily large archives without needing to decompress anything, and it preserves the archive exactly as-is. Reassembling the parts by concatenation produces a byte-identical copy of the original file.

The PKWARE split archive format

The ZIP format, created by Phil Katz in 1989 and standardized as PKWARE's APPNOTE.TXT, includes a native spanning mechanism in its specification. PKWARE's spanning uses special signatures and disk numbers embedded in each local file header and the central directory. However, the simpler byte-level splitting used by HJSplit, GSplit, and this tool is far more widely supported in practice because it requires no ZIP-aware logic to reassemble — a simple cat or binary concatenation suffices.

Zero-copy File.slice() for efficiency

The browser's File.slice() method returns a lightweight Blob reference to a byte range within the file, without copying the data into memory. Splitting a 4 GB archive into 100 parts does not require 4 GB of RAM — each part is a zero-copy view into the original file. The actual bytes are only read when the user downloads a part or requests a bundled ZIP archive. This is the same mechanism browsers use internally for multipart form uploads and HTTP Range requests for video streaming.

Part naming convention

Parts follow the filename.zip.001, .zip.002, .zip.003 naming pattern. The .zip extension is preserved in the part names so that file managers and archive utilities can identify them as split ZIP archives. Three-digit zero-padding supports up to 999 parts. During reassembly, the tool auto-sorts parts by their numeric extension regardless of the order they were added.

Why Use This Tool

Common use cases for ZIP splitting

Splitting ZIP archives is a practical solution for a range of file transfer and storage constraints:

Email attachment limits — most email providers cap attachments at 25 MB. A 200 MB ZIP archive can be split into eight 25 MB parts, sent across separate emails, and reassembled by the recipient. Gmail, Outlook, and Yahoo all enforce this limit as of 2025.
FAT32 file system constraints — USB drives, SD cards, and older external drives formatted as FAT32 cannot store files larger than 4 GB. Splitting a 6 GB archive into 2 GB parts allows transfer on FAT32 media without reformatting to exFAT or NTFS.
Cloud storage upload limits — some services cap individual file uploads at 2 GB or 5 GB. Google Drive's web uploader, for example, limits uploads to 5 TB but recommends files under 5 GB. Splitting circumvents these per-file limits while maintaining archive integrity.
Slow or unstable network connections — uploading one 500 MB file over a flaky connection risks losing the entire upload if it drops. Splitting into 50 MB parts means each part can be uploaded and verified independently, with only failed parts needing retry.
Forum and file-sharing service limits — many forums, Discord servers, and free hosting services restrict individual file sizes to 8 MB, 25 MB, or 100 MB. ZIP splitting is the standard workaround.
Archive distribution — distribute a large dataset across multiple physical media (USB drives, DVDs) or download mirrors. Each recipient gets a subset of parts; concatenation reconstructs the complete archive.

Privacy and security

This tool processes ZIP archives entirely within your browser. No data is transmitted to any server, no temporary copies are created in the cloud, and no analytics track the files you work with. The File.slice() API operates on the browser's internal file handle — even the JavaScript runtime does not hold the full file in memory. For sensitive archives containing legal documents, medical records, financial data, or proprietary source code, local processing eliminates any risk of data exposure during transit.

Verifying archive integrity after reassembly

After reassembling a split archive, compare the SHA-256 hash of the reassembled file against the original to confirm byte-for-byte integrity. Use the Hash Generator or the File Checksum Calculator to compute and compare digests. Any mismatch indicates a corrupted or incomplete part.

Related tools

The Split & Merge Files tool handles any file type with both size-based and line-count splitting. For compressing files before splitting, the GZIP Compress tool and LZMA Compress tool offer different compression algorithms. The Hex Dump Viewer lets you inspect the raw bytes of individual parts to verify their contents.

FAQ

What is the maximum ZIP file size I can split?

There is no hard limit imposed by the tool. It uses File.slice() to create zero-copy byte references for each part, so even multi-gigabyte archives never load entirely into memory. Your browser tab's memory allocation (typically 1-4 GB) is the practical upper bound.

Can I reassemble parts that were split by another tool?

Yes. The reassemble mode concatenates files in numeric order based on their extension (.001, .002, etc.). This works with parts created by any byte-level splitter including HJSplit, GSplit, 7-Zip split archives, or the Unix split command.

Are the split parts still valid ZIP files individually?

No. Each part is a raw byte chunk of the original archive. Only after reassembling all parts in order do you get a valid ZIP file. This is byte-level splitting, not archive-level splitting.

How does the naming convention work?

Parts follow the .zip.001, .zip.002, .zip.003 pattern. The tool strips the .zip extension from the original filename, then appends .zip.NNN for each part. This convention is widely recognized by file splitters and archive managers.

Is my data sent to a server during splitting?

No. All processing happens entirely in your browser using the File API. Your archives never leave your device. You can verify this by disconnecting from the internet — the tool continues to work normally.