⚛️ Degree of Unsaturation Calculator
Enter the atom counts from a molecular formula to calculate its degree of unsaturation (also called the index of hydrogen deficiency), which tells you how many rings and/or pi bonds a molecule contains.
What degree of unsaturation tells you
The degree of unsaturation (DoU), also known as the index of hydrogen deficiency (IHD), is a quick way to determine how many rings and/or multiple bonds (double or triple bonds) a molecule contains just from its molecular formula, before drawing out its structure.
The formula
For a formula containing carbon (C), hydrogen (H), nitrogen (N), and halogens (X = F, Cl, Br, I), the degree of unsaturation is DoU = (2C + 2 + N − H − X) ÷ 2. Oxygen and sulfur atoms do not affect the calculation and can be ignored. Each degree of unsaturation represents either one ring or one pi bond; for example, a benzene ring (C6H6) has a DoU of 4, accounting for the ring plus three double bonds.
Note: This calculator assumes standard valences (carbon tetravalent, nitrogen trivalent, hydrogen and halogens monovalent) and is intended for general organic chemistry education and structure-checking, not as a substitute for full structural analysis.