Science, Tech, Math › Science Gram Molecular Mass Definition Chemistry Glossary Definition of Gram Molecular Mass Share Flipboard Email Print Gram molecular mass is the mass in grams of one mole of sample. zhangshuang, Getty Images Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated July 03, 2019 Definition Gram molecular mass is the mass in grams of one mole of a molecular substance. Gram molecular mass is the same as molar mass. The only difference is that gram molecular mass specifies the mass unit to be used. Gram molecular mass may be reported in grams or grams per mole (g/mol). How to Find Gram Molecular Mass Use the molecular formula to calculate mass. Look up the relative atomic mass of each element in the formula.Multiply the subscript after each element symbol (the number of atoms) by that element's atomic mass. If there is no subscript, it means there is only one atom of that element in the molecule.Add all of the values together to find the gram molecular mass. Example The molecular mass of N2 is 28, so the gram molecular mass of N2 is 28 g.