What is the F90 file format?
A .f90 file contains Fortran source code written in free-form layout - the defining characteristic introduced by the Fortran 90 standard (ISO/IEC 1539:1991). Unlike the older fixed-form .f files, which required code to begin in specific columns inherited from punched-card conventions, free-form .f90 source allows statements anywhere on a line up to 132 characters wide.
Despite the name, the .f90 extension signals layout only - not the language revision. Modern compilers, including gfortran and Intel's ifx from the oneAPI HPC Toolkit, accept Fortran 2023 syntax in .f90 files without any issues.
Fortran remains dominant in high-performance scientific computing. Major weather and climate models, computational fluid dynamics solvers, and finite-element frameworks are written in Fortran and distributed as .f90 source files. The language standard has evolved through Fortran 95, 2003, 2008, 2018, and 2023, each adding object-oriented, parallel, and interoperability features.
A .f90 file is plain ASCII or UTF-8 text with no binary header. Source units - MODULE, PROGRAM, SUBROUTINE, and FUNCTION - form the top-level building blocks. Continuation lines use & at the end of a line, and ! begins a comment to end of line. Compilers produce object files that are linked into executables or shared libraries.
Security & safety
RISK: LOWSource code text file; cannot execute on its own. Risk only if compiled and run. Downloaded .f90 files from untrusted sources should be reviewed before compiling - Fortran code can perform arbitrary system calls.
Format details
in a nutshellPrograms that open F90 files
Windows5 apps
Microsoft Visual Studio
Freemium Requires Intel Fortran or PGI plugin; VS itself has no native Fortran support. 
Intel Fortran Compiler (ifx) - oneAPI HPC Toolkit
Free ifx source.f90 -o output.exe - compile from command line.
GFortran (MinGW-w64 / MSYS2)
Open-source gfortran source.f90 -o output.exe - standard GNU Fortran compiler. 
Visual Studio Code
Free Open .f90 file; install 'Modern Fortran' extension for syntax highlighting and linting. 
macOS2 apps
Linux2 apps
Intel Fortran Compiler (ifx) - oneAPI HPC Toolkit
Free source /opt/intel/oneapi/setvars.sh; ifx source.f90 -o output. Technical details
deep spec| Source layout | Free-form; statements may start at any column, up to 132 characters per line |
| Character encoding | ASCII or UTF-8 (character set is processor-defined per the standard) |
| MIME type | text/x-fortran (also text/plain) |
| Top-level source units | `PROGRAM`, `MODULE`, `SUBROUTINE`, `FUNCTION`, `BLOCK DATA` |
| Continuation syntax | `&` at end of line continues to the next line (free-form style) |
| Comment syntax | `!` introduces a comment to end of line |
| Compiled output | Object files (`.o` / `.obj`), linked into executables or `.a` / `.lib` libraries |
| Primary use domain | Scientific HPC: weather/climate modelling, computational fluid dynamics, finite-element analysis |
| Compiler examples | `gfortran` (GCC), Intel `ifx` (oneAPI HPC Toolkit), Cray `ftn`, NAG Fortran |
| Standard compatibility | `.f90` extension accepted for all Fortran revisions: 90, 95, 2003, 2008, 2018, 2023 |
| Module interface files | Compiled `MODULE` units produce `.mod` files consumed by `USE` statements in other files |
| Preprocessor support | Many compilers accept C-style directives (`#ifdef`, `#define`) in `.f90` files |
| Extension distinction | `.f90` signals free-form layout only; `.f` / `.for` signal fixed-form (Fortran 77 style) |
| Released | 1991 (Fortran 90 standard ISO/IEC 1539:1991) |
| Latest version | Fortran 2023 (ISO/IEC 1539-1:2023); .f90 extension covers any free-form Fortran |
| Open standard | Yes · royalty-free |
| Specification | wg5-fortran.org |
F90 conversions
Community Q&A
asked by usersNo questions yet - be the first to ask about F90 files.
