Osmolality Calculator
Estimate the osmolality of a solution from the molal concentration of solute and how many particles each unit dissociates into.
What osmolality measures
Osmolality is the total concentration of all dissolved particles in a solution, expressed per kilogram of solvent. It matters whenever the number of particles in solution (not just the number of solute molecules) drives an effect, such as osmotic pressure across a membrane.
The formula used
Osmolality (mOsm/kg) = molality (mol/kg) × van’t Hoff factor (i) × 1000. The van’t Hoff factor accounts for dissociation: a non-electrolyte like glucose has i = 1 since it does not split apart in solution, while a strong electrolyte like NaCl has i close to 2 because each formula unit produces two ions (Na+ and Cl-).
- Molality is moles of solute per kilogram of solvent, not per liter of solution.
- This formula assumes ideal, complete dissociation; real solutions can deviate somewhat at higher concentrations.
This tool is intended for general chemistry education and laboratory planning purposes, not for clinical or diagnostic use.