Molality calculator


How to use our molality calculator?

The molality calculator allows you to calculate quickly the molality (not to be confused with molarity). To calculate the concentration of a solute in a solution, set the number of moles of the solute substance. Finally, set the mass of the solvent with the corresponding unity of your value. The calculator will automatically give the molality of the solution in mol/kg.

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What is the molality?

The molality is the amount (number of moles) of solute contained in 1 kilogram of solvent.

Molality formula

So, this definition gives the formula of the molality as follow:

b = nsolute/msolvent


  • b is the molality expressed in moles per kilogram
  • nsolute is the amount of solute in moles
  • msolvent is the mass of the solvent in kg

Molality unit

In the Internation System of units (SI unit), the definition of the molality is in moles per kilogram of solvent (mol/kg).

One mol/kg is also sometimes defined as 1 molal or 1 m. However the term molal and its unit symbol m is obsolete. The mol/kg is the recommended definition of the unit for the molality.

Molality symbol

The molality is defined by the symbol b.

Like explained for the unit, the m symbol (of molal) is obsolete.

Molality vs molarity

The two concepts are the same, they both measures the concentration of a solution. The classical molarity measures the amount of solute per unit of volume of the solvent. However the molality measures the concentration per unit of mass of the solvent. This difference is very important, because the volume can vary in function of the temperature. As a result, this can cause inaccuracies in the case of the molarity.

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