File Split & Join

What it's for

Cut a big file into smaller parts, for an upload or email limit, a small drive, or a transfer that keeps failing, and join the parts back into the original later. Parts are saved as name.001, name.002 and so on. It works on any kind of file, because it only cuts the bytes at set points.

For example, when a service accepts files up to 25 MB and yours is 80 MB, split it into parts of 25 MB, send the four parts, and join them at the other end.

How to use it

Split: choose a file, or drop it on the File to split box, then choose whether to cut it into parts of a size (in MB, where 1 MB is 1,048,576 bytes) or into a number of parts. The list shows every part and its size. Save saves one part; Save all in one ZIP puts them in a ZIP (for files up to 500 MB). The settings are remembered in this browser.

Join: choose all the parts together, or drop them on the Parts to join box. Names ending in .001, .002… are joined by number, and refused if one is missing, two are numbered the same, they come from different files, or the sizes don’t fit (every part but the last the same size, the last no larger). The joined file is saved with the name before the number. Other names are joined in name order, without those checks.

Example

Choose any file of a few MB, set Cut into to this many parts and Number to 3. The list shows yourfile.001 to yourfile.003, the first two the same size. Save all three (or the ZIP and unzip it), choose them under Join, and the file saved is identical to the one you started with.

Good to know

The page holds one file in memory when it makes a ZIP, so very large files are best saved a part at a time. At most 999 parts are made. The parts are plain cuts of the file with no checksum, so joining checks the names and sizes but cannot tell that a part was changed or damaged; compare the joined file with the original (a Hash tool can help). Parts made here can be joined without this site: on macOS and Linux, cat name.0* > name (or cat name.[0-9][0-9][0-9] > name for more than 99 parts) in the folder of the parts; on Windows, copy /b name.001+name.002+name.003 name listing every part. Other splitters’ parts are joined here only if they are plain cuts named .001, .002…; parts with their own headers or archive formats (such as 7-Zip or RAR volumes) need their own program.