Molality (molal.) - Dynamic NPU Manual

Molality (molal.)



Definition in words

Amount-of-substance of component B (solute) divided by mass of system 1 (solvent)

Note: Molality differs from substance content that refers to mass of a system (mixture), whereas for molality it refers only to the mass of a solvent.

Definition by equation

Systematic terms

Molality of component B in system 1

Result type

Rational scale
  • Value sets are positive numerical values
  • Algebraic operations are allowed (a=nb; a≠nb)
Numerical values from 0-∞


fmol/kg, pmol/kg, nmol/kg, μmol/kg, mmol/kg, mol/kg, etc.


Ferard G, Dybkaer R, Fuentes-Arderiu X. Compendium of Terminology and Nomenclature of Properties in Clinical Laboratory Sciences : Recommendations 2016. 1 ed: Royal Society of Chemistry; 2016. 182 p. doi:10.1039/9781782622451.

Laboratory field


Clinical Chemistry

Generic abbreviated
NPU03433  P—Solute; molal.(proc.) = ? mmol/kg
Full result NPU03433 Plasma—Solute; molalality(procedure) = 314 millimol per kilogram
Abbreviated result NPU03433  P—Solute; molal.(proc.) = 314 mmol/kg
Written expression The molality of Solute in Mr. Smith’s plasma is [314] mmol/kg. The measurement is performed according to procedure defined by the laboratory.

Solute refers to all particles in plasma.


NPU database, and
  • Kind-of-property

    • Nominal kind-of-property

    • Kind-of-quantity

      • Unitary kind-of-quantity

        • Rational unitary kind-of-quantity

          • Molality


  • Dybkaer R. Concept system on ‘quantity’: formation and terminology. Accredit Qual Assur. 2013;18(3):253-60.
  • Dybkaer R. ISO terminological analysis of the VIM3 concepts ‘quantity’ and ‘kind-of-quantity’. Metrologia. 2010;47(3):127-34.
Date Term Note
1996-01-01 Molality Term established