Degree of Unsaturation Calculator
Enter the number of carbon, hydrogen, nitrogen, and monovalent halogen atoms in a neutral, closed-shell organic formula. The calculator returns the degree of unsaturation, also known as the double bond equivalent (DBE) or index of hydrogen deficiency (IHD): the number of rings and pi bonds in the molecule.
Last updated: September 26, 2026
Frequently asked questions
What is degree of unsaturation?
It's a count of the total number of rings and pi bonds (from double and triple bonds) in a molecule, calculated from its molecular formula alone, without needing to draw the structure.
Is this the same as double bond equivalent (DBE) or index of hydrogen deficiency (IHD)?
Yes. Degree of unsaturation, double bond equivalent, and index of hydrogen deficiency are three common names for the same calculation and the same result.
How do rings and multiple bonds each count?
A ring counts as 1. A double bond counts as 1. A triple bond counts as 2, since it represents two degrees of unsaturation compared with a single bond.
Why don't oxygen or sulfur appear in the formula?
Oxygen and sulfur are divalent, like the pair of extra hydrogens present in a fully saturated chain of the same carbon count, so adding them doesn't change the hydrogen deficiency. They can be present in the molecule; they just don't need their own term in this equation.
Does one DBE value tell me the exact structure?
No. A given degree of unsaturation is consistent with many different combinations of rings and multiple bonds, and even different molecules entirely. It narrows down possibilities but doesn't identify a unique structure by itself.
Does this work for every type of molecule?
It's built for neutral, closed-shell organic molecules with typical valences. It doesn't reliably apply to ions, radicals, most organometallic compounds, or elements with unusual valence states, and a non-integer result is a sign the formula doesn't fit this model.