# Molality Calculator

Free molality calculator. Calculate molality, moles, or solvent mass using m = moles / kg solvent. Temperature-independent concentration.

## What this calculates

Calculate molality (m) -- the number of moles of solute per kilogram of solvent. Unlike molarity, molality does not change with temperature because it is based on mass, not volume.

## Inputs

- **Solve For** — options: Molality (m), Moles of Solute, Mass of Solvent (kg) — Select which variable to calculate.
- **Molality** (mol/kg) — min 0 — Concentration in moles per kilogram of solvent.
- **Moles of Solute** (mol) — min 0 — Amount of solute in moles.
- **Mass of Solvent** (kg) — min 0 — Mass of the solvent (not solution) in kilograms.

## Outputs

- **Result** — The calculated value.
- **Unit** — formatted as text — Unit of the result.
- **Formula** — formatted as text — Step-by-step calculation.

## Frequently Asked Questions

**Q: What is molality?**

A: Molality (m) is a measure of concentration defined as moles of solute per kilogram of solvent. It is different from molarity, which uses liters of solution. The symbol for molality is lowercase m, while molarity uses uppercase M.

**Q: Why use molality instead of molarity?**

A: Molality is temperature-independent because mass does not change with temperature, while volume does. This makes molality preferred for calculating colligative properties (boiling point elevation, freezing point depression, osmotic pressure).

**Q: Is the solvent mass the same as the solution mass?**

A: No. Solvent mass is only the mass of the solvent (e.g., water), not including the solute. Solution mass = solvent mass + solute mass. This is a common source of errors.

**Q: How do I convert between molarity and molality?**

A: For dilute aqueous solutions, molarity and molality are approximately equal. For concentrated solutions: m = M / (density - M × molar mass / 1000), where density is the solution density in kg/L.

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Source: https://vastcalc.com/calculators/chemistry/molality
Category: Chemistry
Last updated: 2026-04-21