What does dalton mean?
The dalton is a unit of mass used throughout chemistry and biology to express the weights of atoms, molecules, proteins, and other microscopic particles. Defined as exactly one-twelfth of the mass of a neutral carbon-12 atom in its ground state, it is numerically identical to the unified atomic mass unit, often abbreviated u. Because individual molecules are extraordinarily light — a single water molecule weighs about 18 daltons — scientists frequently use multiples such as kilodaltons (kDa) when discussing proteins or large complexes. The unit honours John Dalton (1766–1844), the English chemist and meteorologist whose early-nineteenth-century work established modern atomic theory: the idea that matter consists of discrete atoms combining in fixed ratios. Widely adopted in molecular biology, mass spectrometry, and pharmacology, the dalton gives researchers a convenient shared scale for describing entities far too small to see, making it indispensable to modern science.
A unit of mass equal to one-twelfth of the mass of an unbound neutral carbon-12 atom, used to express atomic and molecular weights; equivalent to the unified atomic mass unit.
"The antibody weighs approximately 150 kilodaltons."
Often encountered as kilodaltons (kDa) or megadaltons (MDa) in biochemistry; formally interchangeable with the unified atomic mass unit (u).
Used attributively or as a proper name to refer to John Dalton (1766–1844), the English chemist who developed modern atomic theory and studied colour blindness.
"Students still learn Dalton's law of partial pressures in introductory chemistry."
Standard plural form; commonly prefixed by SI-style multiples such as kilodaltons (kDa).
"Large protein complexes can exceed several hundred thousand daltons in mass."
Named after a Quaker schoolteacher who couldn't afford university, the dalton now measures everything from hydrogen atoms to antibodies.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of dalton
The dalton takes its name from John Dalton, the English chemist born in 1766 whose atomic theory transformed chemistry in the early nineteenth century. The unit was introduced by twentieth-century scientists as a practical synonym for the unified atomic mass unit, adopting Dalton's name in recognition of his foundational role in establishing that matter is composed of atoms with characteristic relative weights. It shares its conceptual root with the word "atom," which itself derives from the Greek "atomos," meaning indivisible — the very idea Dalton helped revive and refine.
Usage notes
In biochemistry and molecular biology, masses are often given in kilodaltons (kDa) or megadaltons (MDa) because proteins and other macromolecules are far too heavy for plain daltons to be convenient. In physics contexts, "unified atomic mass unit" (u) is often preferred as the formal SI-accepted name, though it denotes the same quantity.
Don't confuse with
"Dulton" is not an established word; dalton is sometimes misspelled this way but always refers to the mass unit or the surname Dalton.