What is a .sit file?
StuffIt Compressed Archive · Archive · Aladdin Systems / Smith Micro · 1987
A .sit file is a StuffIt archive, the standard compressed format of the classic Mac era: 1990s Mac software downloads were almost all .sit (often .sit.hqx). The later .sitx is the StuffIt X successor.
What is a .sit file used for?
StuffIt mattered on the Mac because it preserved the old dual-fork file structure (resource and data forks) that ZIP mangled, so Mac programs survived a download intact. Classic archives start with the bytes SIT! at the file's beginning.
Modern macOS no longer ships anything that opens them. StuffIt Expander still exists as a free download and remains the sure way in; The Unarchiver handles most classic .sit files too, though StuffIt X (.sitx) support elsewhere is spotty.
What opens a .sit file?
The .sit format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list.
Windows
- StuffIt Expander for Windows
- 7-Zip (some classic .sit)
macOS
- StuffIt Expander
- The Unarchiver
Linux
- The Unarchiver (unar)
Open a .sit file step by step
- Confirm the file really is a .sit. Drop it into the WhatFileType identifier, which reads its signature in your browser without uploading anything.
- On Windows, open it with StuffIt Expander for Windows or 7-Zip (some classic .sit).
- On Mac, use StuffIt Expander or The Unarchiver.
- On Linux, try The Unarchiver (unar).
- Still stuck? Convert the .sit to zip, which opens more widely.
Why can't I open my .sit file?
Almost always because no installed app understands StuffIt. Install one of the apps above, or convert the file to a format your existing software already reads. If double-clicking opens the wrong program instead of nothing at all, the file association is set to the wrong app rather than the file being broken.
The other possibility is that the file is not really a .sit at all. Drop it into the file identifier to check it by its bytes instead of its name. Nothing is uploaded.
How to convert a .sit file
You can convert a .sit file to zip, 7z using a conversion tool or the export menu of an app that opens it.
What is the .sit file signature (magic bytes)?
A .sit file starts with the hex bytes 53 49 54 21 00, which read as SIT!. in ASCII. Programs identify StuffIt by those bytes, not by the filename, so a renamed file still gives itself away.
These are the documented signatures for StuffIt. For a full breakdown, see the StuffIt file signature page.
| Hex signature | Offset | ASCII | Note |
|---|---|---|---|
| 53 49 54 21 00 | 0 | SIT!. | classic StuffIt; StuffIt X (.sitx) uses a different header |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .sit file?
A .sit file is a StuffIt archive, the standard compressed format of the classic Mac era: 1990s Mac software downloads were almost all .sit (often .sit.hqx). The later .sitx is the StuffIt X successor.
How do I open a .sit file on a modern computer?
Install the free StuffIt Expander (macOS or Windows) or try The Unarchiver. Both open classic .sit archives; Expander is the safest bet for odd or old variants.
What is the difference between .sit and .sitx?
.sit is the classic StuffIt format from the Mac OS 8/9 era; .sitx is the redesigned StuffIt X format from 2002 with better compression but even less third-party support.
What is a .sit.hqx file?
A StuffIt archive wrapped in BinHex text encoding, the old way to move Mac files through email and early web servers. StuffIt Expander decodes both layers in one go.
Related formats
Sources
Details on this page were checked against authoritative references. How sources are ranked and what is deliberately left out is set out in the methodology.