What is the F file format?
A .f file contains Fortran source code in the fixed-form column layout inherited from 80-column IBM punch cards. Fortran (Formula Translation) was developed at IBM in 1957, making it the oldest high-level programming language still in active production use. The .f extension conventionally signals fixed-form source to compilers - a critical distinction, since column positions carry semantic meaning.
Fixed-form layout rules:
- Column 1: blank = executable line;
C,*, or!= comment - Columns 1-5: statement label
- Column 6: continuation character (any non-blank, non-zero character continues the previous line)
- Columns 7-72: statement body
- Columns 73-80: optional sequence number (ignored by modern compilers)
The .f extension implies FORTRAN 77 fixed-form syntax. Fortran 90 and later introduced free-form source with no column restrictions, which should use .f90, .f95, .f03, or .f08. Compilers such as gfortran and Intel ifx infer the source form from the extension unless overridden with flags like -ffree-form.
Fortran dominates scientific computing: computational fluid dynamics, climate modeling, quantum chemistry, and finite-element analysis all maintain millions of lines of legacy .f code on HPC clusters. The ISO/IEC 1539-1 standard governs the language; the current edition is Fortran 2023.
Security & safety
RISK: LOWPlain text source code. Opening in a text editor or IDE is completely safe. Risk arises only if compiling and running untrusted Fortran code.
Format details
in a nutshell- Generic source file fragment - Some build systems use .f as an abbreviation for arbitrary input files; context-dependent, rare.
Programs that open F files
Windows5 apps
Intel Fortran Compiler (ifx/ifort)
Free ifort source.f -o output.exe (command line); integrates with Visual Studio as a plugin.
Microsoft Visual Studio (with Intel Fortran plugin)
Freemium Install Intel oneAPI HPC Toolkit; VS gains Fortran project type and IntelliSense for .f files.
VS Code + Modern Fortran extension
Open-source Install 'Modern Fortran' extension; provides syntax highlighting, diagnostics, and fortls language server. 
macOS3 apps
TextMate
Open-source Open .f file; TextMate recognizes Fortran syntax. Use as text editor only, not compiler.
Apple Xcode (text editing only)
Free Can open .f as a text file; no Fortran compiler or project template included - use gfortran separately. 
Linux2 apps
gfortran (GCC)
Open-source sudo apt install gfortran; gfortran source.f -o output (fixed-form inferred from .f extension) Technical details
deep spec| Source form | Fixed-form - column-sensitive layout inherited from 80-column punch cards |
| Column semantics | Col 1 = comment flag (C/*/!); cols 1-5 = label; col 6 = continuation; cols 7-72 = code; cols 73-80 = sequence |
| Implied standard | FORTRAN 77 (ISO/ANSI X3.9-1978) - inferred from .f extension by most compilers |
| MIME type | text/x-fortran |
| Encoding | ASCII 7-bit (historical); modern compilers accept UTF-8 in comments and string literals |
| Free-form counterparts | .f90 / .f95 / .f03 / .f08 for Fortran 90+ free-form source (no column restrictions) |
| Compiler flag override | -ffree-form (gfortran) or -free (Intel ifx/ifort) forces free-form parsing of .f files |
| Governing standard | ISO/IEC 1539-1 (current edition: Fortran 2023) |
| Primary domain | Scientific/HPC computing - CFD, climate models, quantum chemistry, finite-element analysis |
| Platform | Linux, Windows, macOS, Unix, HPC clusters (Cray, IBM Power, etc.) |
| Typical size | 1 KB - 2 MB per source unit |
| Alternative fixed-form extensions | .for, .ftn, .f77 (less common; same fixed-form column syntax) |
| Compilation output | Object file (.o) linked into executable or library; no standard bytecode intermediate |
| Released | 1957 (FORTRAN I by IBM); .f extension standardized with FORTRAN 77 (1978) |
| Latest version | Fortran 2023 (ISO/IEC 1539-1:2023); compilers use .f90/.f95/.f03 for newer dialects |
| Open standard | Yes · royalty-free |
| Specification | fortranwiki.org |
F conversions
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