Double Bond Equivalent Calculator (Degrees of Unsaturation)
Enter the number of carbon, hydrogen, nitrogen and halogen atoms in a molecular formula to find the Double Bond Equivalent — the total count of rings and π bonds in the molecule.
Four degrees — possible benzene ring (aromatic)
- 1
Max H for saturated molecule (2C + 2 + N − X)
2 × 6 + 2 + 0 − 0 = 14A fully saturated acyclic molecule with these atoms could hold this many hydrogens. - 2
Hydrogen deficiency (maxH − H)
14 − 6 = 8 - 3
Double bond equivalent (÷ 2)
8 ÷ 2 = 4
How does this calculator work?
DBE = (2C + 2 + N − H − X) / 2. It counts the total number of rings and π bonds in a molecule. A saturated molecule has DBE = 0; each additional ring or double bond adds 1 (a triple bond adds 2). Oxygen and sulfur are ignored; halogens subtract 1 each. DBE = 4 is the classic aromatic (benzene) signature.
Formula
How this is calculated
The Double Bond Equivalent (DBE), also called the Index of Hydrogen Deficiency (IHD) or degrees of unsaturation, counts how many rings and π bonds a molecule contains. A fully saturated acyclic molecule with C carbons and N nitrogens has a maximum hydrogen count of 2C + 2 + N (the CₙH₂ₙ₊₂ rule extended for nitrogen). Each double bond or ring reduces the hydrogen count by 2, so DBE = (MaxH − ActualH) / 2 = (2C + 2 + N − H − X) / 2. Halogens (X) replace one hydrogen each, so they are subtracted; oxygen and sulfur neither add nor subtract, so they do not appear in the formula.
A DBE of 0 means the molecule is fully saturated (no rings, no double bonds). A DBE of 4 is the classic signature of a benzene ring (one ring + three double bonds, all counted together). A DBE of 1 could be a single ring or a single C=C or C=O double bond; a value of 2 could be two double bonds, one triple bond (C≡C contributes 2), or one ring plus one double bond.
The formula assumes all carbon is tetravalent, nitrogen is trivalent, and halogens are monovalent — the standard organic-chemistry model. It does not distinguish between structural isomers (DBE is the same for cyclohexane and hex-1-ene, both DBE = 1). Half-integer results are mathematically possible but indicate an odd-electron (radical) species or an error in the formula.
Frequently asked questions
Oxygen and divalent sulfur replace two hydrogen atoms in the saturated formula but also reduce the maximum hydrogen count by 2, so the two effects cancel. They do not change the degree of unsaturation.
A benzene ring contributes exactly 4 to the DBE: one ring closure plus three C=C double bonds. A DBE of 4 in an aromatic compound is therefore consistent with a single benzene ring.
A DBE of 0.5 indicates an odd-electron species such as a radical or a charged intermediate. In neutral closed-shell organic molecules the DBE is always a non-negative integer; a fractional result usually signals a typo in the formula.
TG we-Calculate Editorial Team. (2026). Double Bond Equivalent Calculator (Degrees of Unsaturation) [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/double-bond-equivalent-calculator
TG we-Calculate Editorial Team. "Double Bond Equivalent Calculator (Degrees of Unsaturation)." TG we-Calculate. 2026. https://we-calculate.com/calculator/double-bond-equivalent-calculator.
TG we-Calculate Editorial Team, "Double Bond Equivalent Calculator (Degrees of Unsaturation)," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/double-bond-equivalent-calculator
@misc{wecalculate_double_bond_equivalent_calculator, title = {Double Bond Equivalent Calculator (Degrees of Unsaturation)}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/double-bond-equivalent-calculator}}, year = {2026}, note = {TG we-Calculate} }
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