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Number of Neutrons Calculator
Find the number of neutrons in an atom’s nucleus from its mass number and atomic number.
What this calculator finds
Every atom’s nucleus is made up of protons and neutrons. The mass number (A) is the total count of protons plus neutrons, while the atomic number (Z) is the number of protons, which also identifies the element.
The formula
Number of neutrons = Mass number (A) − Atomic number (Z). For example, carbon-14 has a mass number of 14 and an atomic number of 6, so it has 14 − 6 = 8 neutrons.
Note: Different isotopes of the same element share the same atomic number but have different mass numbers (and therefore different neutron counts). This tool is for general chemistry education.
Last reviewed August 2026