How would you calculate the mass number of an atom? Chemistry Matter Mass Number 1 Answer Madi Oct 30, 2015 Add the number of neutrons and protons together. Answer link Related questions How do you find mass number of an isotope? What does the difference between the mass number and the atomic number tell us? Why is mass number a decimal? What type of radioactive decay produces no change in mass number? How is the mass number written? What is the nucleon number? What is mass number equal to? What does the mass number tell us? How is mass number related to isotopes? How is the atomic mass number changed by gamma decay? See all questions in Mass Number Impact of this question 2502 views around the world You can reuse this answer Creative Commons License