Open any browser.
Visit the website www.peptideguide.com. On the left side of the page, you should see a list of tabs.
Look for the tab that says "Peptide Mass Calculator."
Click this tab. You will see a chart that lists amino acids and their corresponding codes. For example, if you wanted to find the mass of a molecule that contains alanine and glutamate, you would look for alanine and glutamate on the chart and enter in the letter a and g since they are the corresponding codes for those amino acids.
Input the amino acid code that corresponds to the molecule in question.
Enter the one-letter code or codes into the box at the top of the page. After you input the sequence of amino acid codes, the calculator will tell you the mass of the amino acids in g/mol, which stands for grams per mole.