How to use the file splitter and joiner
- To split a file, choose Split a file into parts, pick the file, then choose to split by size of each part in megabytes or by number of parts, and press Split the file.
- Download each part with its own Download button, or press Download all parts in a ZIP. Part names end in .001, .002 and so on. Write down the SHA-256 fingerprint shown for the original file.
- To join parts, choose Join parts back into one file and add all the parts. The list shows the order they will be joined in, and the tool tells you if a part is missing.
- Press Join and download. Compare the SHA-256 fingerprint shown with the one from the original. If they match, the joined file is identical to the original.
Splitting a 10 MB file
A 10 MB file split into parts of 4 MB gives three parts: 4 MB, 4 MB and 2 MB. Split into 4 parts by number, a 10 byte file gives parts of 3, 3, 3 and 1 bytes, since each part is the file size divided by the count, rounded up. Asking for 6 parts of a 10 byte file gives 5 parts of 2 bytes, because six parts would leave the last one empty.
Part names are the original name plus a number: report.pdf.001, report.pdf.002 and report.pdf.003. The fingerprint of the text hello world, for example, is b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9, and any change to even one byte gives a completely different value.
What a part is
A part is an exact slice of the original bytes. There is no compression, no encryption and no extra header. That makes the parts easy to rejoin with any tool that can append files in order, and it means each part is meaningless on its own, so a part of a photo or a document will not open until the file is joined.
Why splitting is useful and what to watch for
Splitting helps when a service limits the size of each upload or email attachment, or when you need to move a large file in pieces on small drives. The person who receives the parts needs all of them. A missing or repeated part number is reported, and the tool refuses to join an incomplete set rather than produce a broken file.
Splitting does not protect the content. Anyone who gets all the parts can rejoin them. For an archive of several files use the ZIP file creator, to look inside an archive use the unzip tool, and to calculate other fingerprints use the hash generator.
Assumptions and limits
- One megabyte is 1,048,576 bytes. A file can be split into at most 200 parts of at least 1 KB each.
- Files up to 100 MB are accepted, to keep your browser responsive.
- Parts are numbered from 001 and must be joined from the first to the last without gaps.
- The SHA-256 fingerprint is calculated in your browser. It proves two files are identical but says nothing about whether the content is safe.
Frequently asked questions
How do I split a large file into smaller parts?
Choose the file, enter the size of each part or the number of parts, and press Split. Each part downloads as its own file, or all of them in a ZIP, named with .001, .002 and so on.
How do I put the parts back together?
Use the join option and add every part. The tool sorts them by number, checks that none is missing, and saves the original file. You can also join them with any program that appends files in order.
How can I check that the joined file is exactly the original?
Compare the SHA-256 fingerprints. The tool shows one when you split and another when you join, and if the two strings are identical, the files match byte for byte.
Are the parts encrypted or compressed?
No. They are plain slices of the original file, so keep them private if the content is private. Add your own encryption first if you need that.