What Is .inp

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Last updated: April 10, 2026

Quick Answer: A .inp file is a text-based input file format used by engineering and scientific software applications such as ANSYS, ABAQUS, and Mplus to store simulation parameters, model definitions, and configuration data. The format enables engineers and researchers to define finite element models, statistical analyses, and computational simulations using human-readable commands without requiring graphical interface interaction. .inp files remain the standard input method for APDL (ANSYS Parametric Design Language) and are compatible with multiple industrial simulation platforms.

Key Facts

ANSYS APDL uses .inp files as command scripts to define mesh, materials, boundary conditions, and loads for finite element analysis
ABAQUS finite element software treats .inp as its native input format for structural, thermal, and fluid dynamics models
Mplus statistical software requires title, data, and variables command blocks in .inp files for structural equation modeling and latent variable analysis
GAMESS quantum chemistry software uses .inp format to define molecular properties and computational methods for quantum simulations
The .inp format has been the standard text-based input method for finite element analysis since the early 1990s across multiple engineering platforms

Overview

A .inp file is a plain text file used to store input parameters and command scripts for specialized engineering, scientific, and statistical software applications. The most common uses include ANSYS Mechanical APDL (Parametric Design Language), where .inp files function as command scripts containing mesh definitions, material properties, boundary conditions, and loads for finite element analysis. These files allow engineers to programmatically define complex simulations without relying on graphical user interfaces, making them ideal for batch processing, version control, and reproducible analysis workflows.

The .inp format is also widely used in statistical software like Mplus, where it contains structured commands for structural equation modeling, factor analysis, and latent variable analysis. Other scientific applications such as ABAQUS (finite element modeling) and GAMESS (quantum chemistry) employ .inp format for similar purposes—serving as human-readable text files that define the complete setup of a computational model. Because .inp files are plain text, they can be created, edited, and managed with standard text editors, version control systems like Git, and automated scripting tools, making them invaluable for engineering research and production simulations.

How It Works

The .inp file format operates through structured command syntax specific to each software application. Here's how the most common implementations function:

ANSYS APDL Execution: When loaded into ANSYS Mechanical, a .inp file executes a sequence of commands that recreate geometry, mesh, material definitions, and loading conditions. The file can contain commands for preprocessing (defining the model), solving (running the analysis), and postprocessing (extracting results). APDL reads the .inp file line by line, interpreting commands to build the complete finite element model before running simulations.
Mplus Statistical Analysis: Mplus .inp files contain required command blocks (TITLE, DATA, VARIABLE) followed by optional analysis specifications. Each command begins on a new line and ends with a colon, with semicolons separating command options. Mplus reads these structured commands to load data, define variables, specify the statistical model structure, and generate output files (.out) containing analysis results and diagnostic information.
File Portability and Interoperability: .inp files can be exported from graphical interfaces in ANSYS Workbench or created manually by users fluent in APDL syntax. This dual creation method allows both GUI-based designers and command-line scripting experts to produce equivalent models. .inp files maintain compatibility across different ANSYS versions and can be version controlled, allowing teams to track model modifications over time and reproduce analyses on different machines.
ABAQUS and GAMESS Integration: ABAQUS uses .inp files as its primary model definition format, containing node coordinates, element definitions, material properties, and step definitions for multi-step analyses. GAMESS quantum chemistry software similarly uses .inp files to specify molecular geometry, basis sets, and computational method parameters. Both applications parse the .inp syntax to configure their respective analysis engines and generate corresponding output files.

Key Comparisons

File Format	Primary Application	Content Type	Key Advantage
.inp (APDL)	ANSYS Mechanical	Command script with geometry, loads, materials	Direct model control, automation, version control compatibility
.stp / .step	CAD Software (Solidworks, Catia)	3D geometry only (no mesh or loads)	Universal geometry sharing between CAD platforms
.cdb	ANSYS Workbench	Binary database with complete model	Preserves all graphical interface settings and selections
.inp (Mplus)	Mplus Statistics	Structural equation modeling commands	Human-readable statistical syntax, easy version control
.inp (ABAQUS)	ABAQUS FEA	Complete finite element model definition	Industry-standard finite element format, widely compatible
.csv / .txt	General Data Import	Tabular data only	Maximum software compatibility, simple format

Why It Matters

Reproducibility in Engineering: .inp files enable exact reproduction of simulations across different computers and time periods. Engineers can commit .inp files to version control repositories, allowing teams to track every change made to a model and understand the evolution of a design. This capability is essential for regulated industries like aerospace and automotive, where simulation documentation and traceability are mandatory for safety certification.
Automation and Batch Processing: .inp files can be generated programmatically by scripts or AI systems, enabling automated mesh generation, parametric studies, and optimization workflows. Teams can create thousands of variation simulations by modifying .inp files systematically, running batch analyses overnight without human intervention. This automation capability dramatically accelerates design iteration and sensitivity analysis in engineering projects.
Cross-Platform Collaboration: Because .inp files are plain text, they are lightweight and easily shared across teams, platforms, and organizations. Researchers can email .inp files, share them via cloud storage, or include them in research publications. Unlike binary formats or graphical designs, .inp files remain readable by humans and compatible with tools from 1990s ANSYS versions through current 2025 releases, ensuring long-term accessibility.
Integration with Scientific Workflows: .inp files integrate seamlessly with Python scripts, MATLAB programs, and shell automation tools. Scientists can generate .inp files from simulation parameters stored in databases, run analyses automatically, and parse output files to feed results into post-processing pipelines. This integration capability has made .inp format the backbone of computational research infrastructures supporting machine learning-assisted engineering and data-driven design optimization.

.inp files represent over three decades of industry standardization in computational engineering and scientific analysis. Their continued adoption across ANSYS, ABAQUS, Mplus, GAMESS, and dozens of specialized simulation tools demonstrates their value as a durable, practical format for capturing the complete specification of complex computational models in human-readable form.