Molecular Weight Calculator

Calculates the molecular weight and percent composition of chemical formulas and amino acids.


This program can calculate the molecular weight and percent composition of chemical formulas and amino acids, providing a graphical user interface to edit the formulas and parsing options. It recognizes user-definable abbreviations, custom elemental isotopes, and can display up to 20 compounds simultaneously. It also includes a Mole/Mass Converter, Formula Finder, Capillary Flow Modeler, Amino Acid Notation Converter, Peptide Sequence Fragmentation Modeler, and built-in calculator.

See also the .NET DLL version of the Molecular Weight Calculator


Software Instructions

The desktop version of the Molecular Weight Calculator is written in VB6. It successfully runs on Windows XP, Windows 7, and Windows 8.

Screenshot: Main Screen

Screenshot: Percent Composition

Screenshot: Percent Solver

Screenshot: Mole/Mass Converter

Screenshot: Amino Acid Notation

Screenshot: Formula Finder

Screenshot: Peptide Frag

Screenshot: Ion Plot

Screenshot: Iso Abundance

Screenshot: Capillary Flow Calculator


All publications that utilize this software should provide appropriate acknowledgement to PNNL and the Molecular-Weight-Calculator-VB6 GitHub repository. However, if the software is extended or modified, then any subsequent publications should include a more extensive statement, as shown in the Readme file for the given application or on the website that more fully describes the application.


These programs are primarily designed to run on Windows machines. Please use them at your own risk. This material was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the United States Department of Energy, nor Battelle, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness or any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.

Portions of this research were supported by the NIH National Center for Research Resources (Grant RR018522), the W.R. Wiley Environmental Molecular Science Laboratory (a national scientific user facility sponsored by the U.S. Department of Energy’s Office of Biological and Environmental Research and located at PNNL), and the National Institute of Allergy and Infectious Diseases (NIH/DHHS through interagency agreement Y1-AI-4894-01). PNNL is operated by Battelle Memorial Institute for the U.S. Department of Energy under contract DE-AC05-76RL0 1830.

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