# What is File compression?

File compression reduces the size of data, either losslessly so the original can be rebuilt exactly, or lossily by discarding detail people are unlikely to notice.

_Source: https://sharelargefilesfree.com/what-is-file-compression · Updated 2026-10-13_

**Quick answer:** File compression reduces the size of data, either losslessly so the original can be rebuilt exactly, or lossily by discarding detail people are unlikely to notice.

## File compression explained

File compression is any method of making data take up less space. It works by finding patterns and redundancy. **Lossless** methods, like ZIP or PNG, give you back every original byte. **Lossy** methods, like JPEG, MP3 and most video codecs, throw away some information to make files much smaller.

Most photos, music and videos are already lossy-compressed. That is why zipping them does little, and why compressing them again can reduce quality.

For sending, you have two choices: shrink the file (and accept some loss), or keep the original and use a service that handles large files without re-compressing them.

## Lossless vs lossy at a glance

| | Lossless | Lossy |
| --- | --- | --- |
| Examples | ZIP, 7z, PNG, FLAC | JPG, HEIC, MP3, AAC, H.264, HEVC |
| Size saving | Modest, depends on the content | Large |
| Original can be restored exactly | Yes | No |
| Best for | Documents, archives, master files | Photos, music and video for viewing and sharing |

## Worked example: three ways to send a 2 GB video

1. **Zip it:** the ZIP is still about 2 GB, because the video is already compressed. No real gain.
2. **Compress the video:** file size follows bitrate, so halving the bitrate makes it about 2 GB ÷ 2 = 1 GB. It uploads in half the time, with some quality loss.
3. **Send the original with a link:** the full 2 GB is delivered unchanged, as long as it fits within 20 GB. Best quality, longest upload.

If quality matters, option 3 is usually right. If the recipient is on a slow connection or only needs a preview, option 2 is kinder.

## Tips for compressing without regret

- Always compress a copy and keep the original.
- Compress once from the original, not again from an already compressed copy.
- Resize images to the size they will actually be shown at before compressing them.
- Check the result on a large screen before sending it to a client.

## Frequently asked questions

### Can I compress a file without losing quality?

Yes, with lossless compression such as ZIP, but it saves little on photos and videos that are already compressed.

### Do messaging apps compress my files?

Many do, especially for photos and videos. Sending as a document or using a download link avoids that.

### Why is my ZIP bigger than the original files?

With files that are already compressed, such as videos and JPGs, the archive's own overhead can make the ZIP very slightly larger. It is harmless.

### How do I compress a video for email?

Email limits are usually around 20 to 25 MB, so only short clips fit even after heavy compression. A download link is usually the better option.