Protons Neutrons Electrons Calculator
Enter an element (or an isotope such as C-14), its mass number and charge to find the number of protons, neutrons and electrons. You also get the isotope notation, the neutron-to-proton ratio and a particle mass breakdown.
Last updated:
Symbol, name, atomic number, or isotope form like C-14 / 235U
Protons + neutrons. Leave empty to use the rounded atomic weight
0 for a neutral atom, 2 for a 2+ ion, -1 for a 1− ion
How to use the Protons Neutrons Electrons Calculator
- Enter the element as a symbol, name, atomic number or isotope like C-14.
- Enter the mass number (protons + neutrons) of the isotope you need.
- Enter the charge: 0 for a neutral atom, a positive number for a cation, a negative number for an anion.
- Read the counts of protons, neutrons and electrons with the isotope notation.
- Copy the results or download the particle table as CSV.
Formulas for protons, neutrons and electrons
| Particle | Formula | Example: ⁵⁶₂₆Fe³⁺ |
|---|---|---|
| Protons | p = Z (atomic number) | 26 |
| Neutrons | n = A − Z | 56 − 26 = 30 |
| Electrons | e = Z − charge | 26 − 3 = 23 |
| Mass number | A = p + n | 26 + 30 = 56 |
The atomic number fixes the element; changing the neutron count gives a different isotope of the same element, and changing the electron count gives an ion.
Common isotopes and ions
| Species | Protons | Neutrons | Electrons |
|---|---|---|---|
| Hydrogen-1 (protium) | 1 | 0 | 1 |
| Hydrogen-2 (deuterium) | 1 | 1 | 1 |
| Carbon-12 | 6 | 6 | 6 |
| Carbon-14 | 6 | 8 | 6 |
| Oxygen-16 | 8 | 8 | 8 |
| Na⁺ (sodium-23) | 11 | 12 | 10 |
| Cl⁻ (chlorine-35) | 17 | 18 | 18 |
| Fe²⁺ (iron-56) | 26 | 30 | 24 |
| Uranium-238 | 92 | 146 | 92 |
Particle masses used in the breakdown table: proton 1.007276 u, neutron 1.008665 u, electron 0.000549 u (CODATA). The sum is slightly larger than the real atomic mass because of the nuclear binding energy (mass defect).
Frequently asked questions
How do you find the number of protons?
The number of protons equals the atomic number Z, which identifies the element. Every carbon atom has 6 protons and every iron atom has 26, whatever the isotope or charge.
How do you calculate the number of neutrons?
Subtract the atomic number from the mass number: N = A − Z. Carbon-14 has 14 − 6 = 8 neutrons, and uranium-235 has 235 − 92 = 143 neutrons.
How do you find the number of electrons in an ion?
Electrons = protons − charge. A neutral atom has as many electrons as protons. Na⁺ has 11 − 1 = 10 electrons, and Cl⁻ has 17 − (−1) = 18 electrons.
What is the difference between mass number and atomic mass?
The mass number A is a whole number count of protons plus neutrons in one specific isotope. The atomic mass (standard atomic weight) on the periodic table, such as 35.45 for chlorine, is the average mass of all natural isotopes in atomic mass units, so it is usually not a whole number.
What is isotope notation?
Isotope (nuclear) notation writes the mass number as a superscript and the atomic number as a subscript to the left of the symbol, e.g. ¹⁴₆C for carbon-14. A charge goes at the top right, as in ²³₁₁Na⁺. Hyphen notation simply writes the name and mass number, carbon-14.
What happens if I leave the mass number empty?
The calculator rounds the element's standard atomic weight to the nearest whole number (for example 55.845 → 56 for iron). That matches the most common isotope for many elements but not all (chlorine-35 and -37, bromine-79 and -81), so enter the mass number when you need a specific isotope.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.