Degree of Unsaturation Calculator

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 know anything about 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 (an ether) neither adds nor removes hydrogens, and the same is true of sulfur.

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 the C=O in acetone)
• 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, and the formula cannot distinguish between them without structural information.

Benzene (C6H6): DoU = (12 + 2 - 6) / 2 = 4. Three double bonds plus the ring.