The latest version of the C3D documentation provided via the first two links below. The documentation is currently being frequently updated to document various aspects of the internal format for end-users and programmers. You can verify the current release date by visiting the Help page link above which will display the current release date of the downloadable PDF manual and CHM help files. Monitoring the default help page via an on-line website monitor will keep you up to data with any changes to the documentation.

C3D User Guide - PDF

This is the current release of the C3D User Guide which documents the C3D format in detail so that everyone can understand the details of the format and potentially write software to access or create C3D files. It is recommended that anyone working with C3D files reads this manual to understand the contents and structure of the C3D format.


This is compiled help (.CHM) version of the C3D User Guide that is generated from the same documents as the PDF C3D User Guide. It can be downloaded and distributed with any application that supports C3D files. Note that when the file is downloaded, you may need to set the file properties to unblock access before the help file contents can be displayed.

Calculating Analog Scale Parameters

An open XML spreadsheet written by Motion Lab Systems that calculates the C3D Analog Scale parameters for AMTI (TYPE2 and TYPE-4) force plates, Kistler (TYPE-3) force plates, Load Cells, and other analog signal sources.  The spreadsheet supports all ADC resolutions and input voltage ranges, and enables the user to investigate and calculate C3D scale factors while documenting the mathematics. Updated 19-Apr, 2020.

Original C3D specification

This is a PDF version of the original text file that documented the C3D file format as written by Andrew Dainis for the AMASS software package, released in the mid 1980's.  This software description has largely been superceded by the C3D Technical User manual which should be used as a reference for all new applications. This document is included for historical reference purposes.

Free C3D icon images

A zip file containing images provided by Motion Lab Systems that are available royalty free at no charge for any application that accesses or creates C3D files. These can be associated with the biomechanics C3D file type when the application is installed to provide all users with a common visual environment.

AMASS C3D Reference Chapter

This is the C3D format chapter from the ADTech Motion Analysis Software System (AMASS) Reference Manual, released in 1994, and containing the description of the C3D file generated by the AMASS applications running in the environment that generated the C3D file from the Oxford Metrics RSX system video data.

C3D User Guide - 2008

The 2008 revision of the C3D User Guide was the last version that included descriptions of some variables used in gait analysis, and stored in a C3D file by manipulating the 3D marker location format. This is a storage method that uses the C3D format, but is not part of the C3D format definition.