updated on Aug. 14, 2016


Getting started


You can download the installation package here.


Unzip the package "fw.zip", execute "setup.exe" and follow instructions of the installer.


Double-click the "FormulaWeight2016" icon on the Desktop.

How to use

If you want to calculate the molecular weight of C2H5OH, click buttons as follows.

"C" - "2"- "H" - "5" - "O" - "H"- "="

The the number, "46.07" will be shown in the text box at the right bottom corner of the application window.
Numbers from "1" to "9999" can be entered for each element.
When you want to terminate the software, click the "exit" button.
You can delete the last input by clicking the "c" button.
Click the "ac" button to clear all inputs.


Atomic weights are from the periodic table and related documents in Chemistry & Chemical Industry (Kagaku-to Kogyo), Vol.69, No.4 (2016) published by Chemical Society of Japan (CSJ). The CSJ documents are based on the information from IUPAC.

No stable isotopes are known for some heavy elements like Ra (radium). Thus an atomic mass number of one of the isotopes is used in this software. You can find whether it is the case or not by putting the mouse cursor on each button. The tool tip appears and the atomic weight of the unstable element is shown in parenthesese like [226].

Distribution of isotopes of some element scatters from sample to sample over accuracy of today's technology. Since the atomic weight of an element is proportional to the average of mass of its stable istopes, the measured "atomic weight" depends on sample. In 2009 IUPAC started to show the variation range of the measurement on available samples for some elements. Following twelve elements are included in such elements at the time of 2016.

H,Li,B,C,N,O,Mg, Si,S,Cl,Br, Tl

Now FormulaWeight2016 follows this direction and the minimum and manimum numbers of the "atomic weight" are shown when the mouse cursor is on the buttons of these elements. In case of "H", for example, that is as follows.

[1.00784, 1.00811]

Please consult the document below for more detal.

IUPAC Inorganic Chemistry Division, CIAAW: Atomic Weights of the Elements 2009, Pure Appl. Chem. 83 (2011) 359.

For calculation of a formula/molecular weight, however, a signle value with significant figures of four digits is used for each element. The calculation is just a sum of atomic weights rounded to four digits. You should consider significant figures carefully when you use the result for your study.