How to Split a File That's Too Big to Send

Sometimes a file is just too big. A 3GB project archive, a long raw video, a virtual machine image. It's over the upload limit of whatever service you're using, and compressing it won't help much because it's mostly already compressed.

One option is to split it into smaller pieces, send those, and have the recipient join them back together. It's a little old-fashioned, but it works reliably.

Before you split: can you avoid it?

Splitting adds a step for the recipient, so check the easier routes first:

• Can you shrink it? Videos especially can often be made much smaller. Re-encoding a 4K phone video to 1080p can cut it by 70-80%.
• Does it all need to go? Maybe the recipient only needs the final exports, not the whole project folder with caches and previews.
• Can it be several separate files? If it's a folder of videos, sending them as individual uploads is simpler than splitting one archive.

If none of that works, split it.

Splitting with 7-Zip (Windows)

1. Right-click the file or folder → 7-Zip → Add to archive...
2. Choose a format. ZIP is the most compatible, 7z compresses better.
3. Find the box labeled Split to volumes, bytes.
4. Type a size, such as 900M for 900MB parts. Stay a little under the limit you're working with.
5. Click OK.

You'll get files named like this:

• project.7z.001
• project.7z.002
• project.7z.003

Send all of them.

Splitting on Mac

Keka (free) can create split archives. In its settings, set a split size before compressing. The result is a set of numbered parts, the same as with 7-Zip.

If you're comfortable in Terminal, the built-in split command also works, for example split -b 900m bigfile.mov part_. But the recipient then needs to rejoin them with a command too, so an archive tool is friendlier for most people.

Putting it back together

This is the part to explain clearly to the recipient, because it's where things go wrong.

1. Download all the parts into the same folder.
2. Don't rename any of them.
3. Open only the first part (the .001 file) with 7-Zip, Keka or The Unarchiver.
4. Extract. The tool finds the other parts automatically.

If a part is missing or incomplete, extraction will fail with an error, usually naming the part it couldn't find.

What to write in your message

Spell it out. Something like:

"The file was too big to send in one go, so I've split it into 3 parts. Please download all three into the same folder, then open the one ending in .001 with 7-Zip (free, 7-zip.org) and extract. It'll combine them automatically."

That one paragraph heads off most problems.

A few practical tips

• Verify the parts. For really important transfers, send a SHA-256 checksum of the original file so the recipient can confirm the rejoined result matches exactly.
• Use consistent part sizes. It makes it obvious if one part is incomplete, because it'll be smaller than the others (except the last one, which is naturally smaller).
• Don't make too many parts. Twenty parts means twenty downloads. Go as close to the limit as you safely can.
• Mind the expiry. If you're using temporary links, the recipient needs to download every part before any of them expire.

When splitting isn't the answer

If you're regularly moving files of tens of gigabytes, splitting gets tedious on both ends. At that point it's worth looking at tools designed for very large transfers, syncing a shared cloud folder over time, or, for truly huge data, the old-fashioned option of a physical drive in the mail.

For the occasional oversize file, though, a split archive and a clear message will do the job.