Degree of Unsaturation Calculator
Calculate degree of unsaturation for any organic molecule.
Enter carbon, hydrogen, nitrogen, and halogen counts to find rings and double bond equivalents.
The Degree of Unsaturation (DoU), also called the Index of Hydrogen Deficiency (IHD) or Double Bond Equivalents (DBE), tells you how many rings, double bonds, and triple bonds are present in an organic molecule based only on its molecular formula — before you even know its structure.
DoU = (2C + 2 + N - H - X) / 2
Where C = carbons, H = hydrogens, N = nitrogens, and X = halogens (F, Cl, Br, I). Oxygen and sulfur do not appear in the formula because they do not change the hydrogen count — adding an oxygen atom between two carbons (ether) neither adds nor removes hydrogens.
What each DoU value means:
- DoU = 0: Fully saturated, no rings or multiple bonds (e.g., hexane C6H14)
- DoU = 1: One ring or one double bond (e.g., cyclohexane or benzaldehyde’s C=O)
- DoU = 2: Two rings, two double bonds, or one triple bond
- DoU = 4: Benzene ring (counts as 3 double bonds + 1 ring = 4)
- DoU = 5+: Naphthalene, steroids, or polycyclic structures
The result must be a non-negative integer or half-integer. A fractional result (0.5, 1.5) may indicate a radical or an error in the formula. A negative result means the formula is invalid.
Practical example: glucose (C6H12O6). DoU = (2×6 + 2 + 0 - 12 - 0) / 2 = (12 + 2 - 12) / 2 = 1 Glucose has one ring (pyranose form) or one double bond (open-chain aldehyde). Both are correct — the formula cannot distinguish between them without structural information.
Benzene (C6H6): DoU = (12 + 2 - 6) / 2 = 4. Three double bonds plus the ring.