Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
Definition
A dalton (Da) is a unit of mass used to express atomic and molecular weights. One dalton is approximately equal to the mass of a hydrogen atom, which is about 1/12th the mass of a carbon-12 atom.
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The dalton is named after John Dalton, an English chemist and physicist known for his work on atomic theory.
1 Da is approximately equal to 1.66053906660 x 10^{-27} kilograms.
It is commonly used in biochemistry and molecular biology to express the masses of proteins, nucleic acids, and other large biomolecules.
The unified atomic mass unit (u or amu) is equivalent to the dalton; both are used interchangeably in scientific literature.
A molecule's molecular weight in daltons can be calculated by adding up the atomic masses (in Da) of all its constituent atoms.
The weighted average mass of an atom's isotopes measured in atomic mass units (amu).
Molecular Weight: The sum of the atomic weights of all atoms in a molecule, often expressed in daltons.
Unified Atomic Mass Unit (u): A standard unit for measuring atomic and molecular masses, equivalent to one-twelfth of the mass of a carbon-12 atom; interchangeable with the dalton.