The “File not found” LaTeX error means your document uses a package that is not installed on your system. LaTeX looked for a .sty file, could not find it, and stopped. The fix depends on which LaTeX environment you are using: Overleaf, TeX Live, or MiKTeX.
What you see:
! LaTeX Error: File `siunitx.sty' not found.
Type X to quit or to proceed,
or enter new name. (Default extension: sty)
l.8 \usepackage{siunitx}
The filename before .sty is the package name. In this example, the siunitx package is not installed.
Quick answer
How to install the missing package:
- Overleaf: The package is either misspelled or does not exist on CTAN. Overleaf has all CTAN packages pre-installed
- TeX Live: Run
tlmgr install packagenamein the terminal - MiKTeX: Open MiKTeX Console, go to Packages, search for the name, and install. Or enable auto-install
If the .sty file is not on CTAN (it is a custom file from a journal or conference template), place it in the same directory as your .tex file.
Overleaf: The Package Is Misspelled or Custom
Overleaf has every CTAN package pre-installed. If you see “file not found” in Overleaf, it is not a missing installation. It is one of two things:
The package name is misspelled. \usepackage{amsmth} fails because the correct name is amsmath. Check the exact spelling on CTAN.
The .sty file is custom. Some journal and conference templates include their own .sty files that are not on CTAN. If you downloaded a template ZIP that includes .sty files, upload those files to your Overleaf project in the same directory as your .tex file. Overleaf will find them automatically.
TeX Live: Install With tlmgr
TeX Live uses tlmgr (TeX Live Manager) to install packages. Open a terminal and run:
sudo tlmgr install siunitx
Replace siunitx with the package name from your error message. On some systems you need sudo for system-wide installation. On others, tlmgr install siunitx works without it.
If tlmgr says the package is not found: The CTAN package name sometimes differs from the .sty filename. For example, the booktabs.sty file is part of the booktabs package, but tabularx.sty is part of the tools bundle. Search CTAN to find the correct package name: tlmgr search --global --file siunitx.sty will tell you which package contains the file.
If tlmgr itself is not found: Your TeX Live was likely installed through your operating system’s package manager (apt, yum, pacman) rather than directly from TUG. In that case, install packages through your OS package manager instead: sudo apt install texlive-science on Ubuntu/Debian, for example.
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MiKTeX: Auto-Install or Manual Install
MiKTeX can install missing packages automatically during compilation. If this is not happening, enable it:
Open MiKTeX Console. Go to Settings. Under “You can choose whether missing packages are to be installed automatically,” select “Always.” MiKTeX will now download and install any missing package the first time your document references it.
If you prefer manual control, go to the Packages tab in MiKTeX Console, search for the package name, and click Install.
If MiKTeX cannot find the package: Click “Check for updates” first. MiKTeX’s package database may be out of date. After updating, search again.
Custom .sty Files From Templates
Journal and conference templates often include custom .sty files that are not on CTAN. IEEE’s IEEEtran.cls, Springer’s sn-jnl.cls, and ACM’s acmart.cls are all examples. If you see “file not found” for a class or style file that came with a template:
Place the .sty or .cls file in the same directory as your .tex file. LaTeX searches the current directory first. If you are using Overleaf, upload the file to your project root. If you are submitting to a journal’s Editorial Manager, tag the .sty/.cls file as “Manuscript” so the compiler can find it.
For other common LaTeX errors, see our complete guide to LaTeX compilation errors. The Overleaf documentation also covers this error with additional examples for their platform.
Frequently Asked Questions
Overleaf has every CTAN package pre-installed, so a “file not found” error in Overleaf means either the package name is misspelled in your \usepackage{} line, or the file is a custom .sty or .cls that came with a journal/conference template and is not on CTAN. Check the spelling against the CTAN page, or upload the missing file to your Overleaf project.
Run tlmgr search –global –file filename.sty in the terminal, replacing filename.sty with the file from your error message. This searches the entire TeX Live repository and tells you which package contains that file. The package name is not always the same as the .sty filename.
Open MiKTeX Console, go to Settings, and under the option for installing missing packages, select “Always.” MiKTeX will then automatically download and install any package your document needs during compilation. If a package still fails to install, click “Check for updates” first to refresh the package database.
