Molecular Mass Calculator

by Christoph Gohlke

This form calculates the molecular mass (average, monoisotopic, and nominal), the elemental composition, and the mass distribution spectrum of a molecule given by its chemical formula, relative element weights, or sequence.

Calculations are based on the isotopic composition of the elements. Mass deficiency due to chemical bonding is not considered.


Formulas are case sensitive and ’+’ denotes the arithmetic operator, not an ion charge.


Because this service is provided free of charge, there is no warranty for the service, to the extent permitted by applicable law. The service is provided "as is" without warranty of any kind, either expressed or implied, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose. The entire risk as to the quality and performance is with you.


Molecular Mass Calculator version 2018.5.29 by Christoph Gohlke. Source code is available at,, and