Molality Calculator

Calculate the molality of a solution by entering the amount of solute and the mass of solvent below.

Amount of Solute:

mol mmol μmol nmol pmol

Mass of Solvent:

mg g kg oz lb

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Molality:

 

mol/kg

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Joe Sexton

Joe is the creator of Inch Calculator and has over 20 years of experience in engineering and construction. He holds several degrees and certifications.

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Teresa Michelsen, PhD

Teresa is a chemistry expert with a PhD in environmental science, a Master's degree in earth, atmospheric, and planetary sciences, and Bachelor's degree in chemistry.

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How to Calculate Molality

Molality represents the concentration of a compound in a solution measured as the amount of the substance in moles divided by the mass of the solute in kilograms. Molality is often expressed in moles per kilogram, or mol/kg, and is denoted using the letter m.

First used in 1923, molality is different from molarity in that molality is the moles of the solute in 1 kg of the solvent, while molarity is the moles of the solute in 1 L of the solvent.^[1]

If the solvent is water, molality and molarity will be the same since 1 L of water weighs 1 kg.

In general, both of these terms are used to prepare and label standard liquid solutions that are frequently used in a laboratory. Both molality and molarity describe the strength of a chemical in solution; for example, a 2M solution is twice as concentrated as a 1M solution.

Molality Formula

Since it’s a ratio, you can calculate molality using the following formula:

molality (m) = moles of solute / kilograms of solvent

Thus, the molality m is equal to the amount of substance of solute in moles divided by the mass of solvent in kilograms.