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CHEMISTRY · CALCULATE · UNDERSTAND

Oxidation Number Calculator

Find an element's oxidation number from a formula and explicit net charge, with selected introductory rules and exceptions.

General chemistry — rule-based, introductory scope

Enter your values

Use a decimal point or scientific notation (1e-3). Choose units before calculating.

Enter an uncharged formula. Enter ionic charge in the separate field.
Choose the element whose oxidation number is unknown or supplied.
Use a whole number in elementary-charge units; for example, SO4²⁻ is -2.
Ionic charge is reported as a whole number of elementary charges.
Try an example

Calculations run on your device. No account, name or email is required.

Your result

Enter your values and press Calculate to see your answer and all five solution steps.

Σ(nᵢ × ONᵢ) = q

Common Mistakes

  • Do not use the ion's total charge as the oxidation number of every atom; the sum, including subscripts, equals the charge.
  • Do not apply O = −2 blindly: peroxides, KO₂, and OF₂ are supported exceptions.
  • An average from a formula, such as Fe3O4 or Na2S2O3, is not proof that every atom has that same oxidation number.

Assumptions and limitations

  • Supported rule-based scope: elemental substances; explicit-charge ions; Group 1/2 metals; Al, Zn, Cd, Ag; H, O, F and simple halogen rules; and the named NaH, H2O2, Na2O2, OF2, and KO2 cases.
  • It does not determine every organic, coordination, covalent, mixed-valence, oxygen-fluorine, hydrate, or polyatomic-ion-containing compound. When more than one independent unknown remains, it rejects the input rather than inventing an oxidation number.
  • Formula charge is entered separately and must be an integer in e. Formula notation with a written charge, hydrate dots, and coefficients is intentionally outside the parser scope.

Σ(nᵢ × ONᵢ) = q

Learn More

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Scientific references

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