Degree of Unsaturation Calculator (IHD / DBE)
The degree of unsaturation (DoU), also called the index of hydrogen deficiency (IHD) or double bond equivalent (DBE), tells you how many rings and π bonds are in an organic molecule. Enter the atom counts from the molecular formula to calculate it instantly.
Four degrees: consistent with a benzene ring (3 double bonds + 1 ring).
- 1
2C + 2
2 × 6 + 2 = 14 - 2
Numerator (+ N − H − X)
14 + 0 − 6 − 0 = 8 - 3
Degree of unsaturation
8 ÷ 2 = 4Each unit is one π bond or one ring closure.
How does this calculator work?
DoU (IHD/DBE) = (2C + 2 + N − H − X) / 2. Each unit represents one π bond (double bond = 1, triple bond = 2) or one ring. O and S do not appear — they are divalent and do not change the hydrogen count. A result of 4 is consistent with a benzene ring.
Formula
How this is calculated
The formula compares the actual number of hydrogen atoms in a molecule to the number that a fully saturated, acyclic molecule with the same number of carbons would have (C_nH_{2n+2} for pure hydrocarbons). Each degree of unsaturation corresponds to either one π bond (a double bond = 1 DoU, a triple bond = 2 DoU) or one ring closure (which also removes two hydrogens from the saturated count).
Nitrogen atoms each add one to the hydrogen count of the saturated reference (because N is trivalent and allows one extra H when saturated), so N appears with a +1 coefficient. Halogens each replace a hydrogen, so they count like H and appear with −1. Oxygen and sulfur are divalent and do not change the hydrogen count, so they do not appear in the formula at all.
A DoU of 4 is a classic diagnostic: it is consistent with a benzene ring (3 double bonds + 1 ring = 4). A DoU of 0 means a saturated acyclic molecule (like an alkane). A half-integer result (e.g. 0.5) indicates an odd-electron species such as a radical, which is unusual for stable molecules — double-check the molecular formula in that case.
Frequently asked questions
No. Oxygen (and sulfur) are divalent and do not appear in the DoU formula. For example, CH3OH (methanol, DoU = 0) and C2H6O (ethanol, DoU = 0) both have zero unsaturation despite containing oxygen.
It is consistent with a benzene ring, which has 3 double bonds and 1 ring (total 4 DoU). Any other combination of 4 π bonds and/or rings also gives DoU = 4, so it is a necessary but not sufficient test for aromaticity.
No — a negative result means the molecular formula cannot correspond to a neutral organic molecule with standard valences. It usually indicates a typo in the formula (too many H, too few C) or an incorrect atom count.
Also known as
TG we-Calculate Editorial Team. (2026). Degree of Unsaturation Calculator (IHD / DBE) [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/degree-of-unsaturation-calculator
TG we-Calculate Editorial Team. "Degree of Unsaturation Calculator (IHD / DBE)." TG we-Calculate. 2026. https://we-calculate.com/calculator/degree-of-unsaturation-calculator.
TG we-Calculate Editorial Team, "Degree of Unsaturation Calculator (IHD / DBE)," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/degree-of-unsaturation-calculator
@misc{wecalculate_degree_of_unsaturation_calculator, title = {Degree of Unsaturation Calculator (IHD / DBE)}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/degree-of-unsaturation-calculator}}, year = {2026}, note = {TG we-Calculate} }
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