Oxidation Number Calculator

Work out oxidation number instantly with clear inputs, formula shown and shareable results.

About Oxidation Number Calculator

Oxidation states must sum to the overall charge. Oxygen is assigned -2 and hydrogen +1 in ordinary compounds, so the central atom absorbs whatever is left over, divided between however many central atoms there are. For sulfate, charge -2 with four oxygens gives (-2 + 8)/1 = +6 for sulfur.

Formulas

Charge balance

n x state + (-2 x oxygens) + (+1 x hydrogens) = overall charge

Central state

state = (charge + 2.oxygens - hydrogens) / n

Worked example

With the default values below, Oxidation Number Calculator returns Oxidation State Of The Central Atom of 6.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Overall charge on the species: -1
Oxygen atoms in the formulaminimum 0: 4
Hydrogen atoms in the formulaminimum 0: 1
Central atoms sharing the balanceminimum 1: 1

Results

Oxidation State Of The Central Atom: 6.00
Contribution From Oxygen: -8.0
Contribution From Hydrogen: 1.0
Read As: +6 on each central atom

Step by step

1Values used
2Charge balance
3Central state
4Oxidation State Of The Central Atom= 6.00
5Contribution From Oxygen= -8.0
6Contribution From Hydrogen= 1.0
7Read As= +6 on each central atom

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

When is oxygen not -2?

In peroxides it is -1, in superoxides -1/2, and bonded to fluorine it is positive. Those cases need the exception applied by hand.

Can an oxidation state be fractional?

Yes. In Fe3O4 iron averages +8/3 because the structure contains both Fe(II) and Fe(III).