Osmotic Pressure Calculator
Use solution molarity, temperature, and van't Hoff factor to estimate osmotic pressure in atm and kPa.
Use dissociation factor (2 for NaCl, 3 for CaCl2, etc.).
Osmotic pressure
4.891 atm
Osmotic pressure
495.542 kPa
How to Use This Calculator
Determine molarity
Calculate the solute molarity in mol/L for the solution of interest.
Estimate van't Hoff factor
Count the number of particles the solute produces upon dissociation. Non-electrolytes use 1.
Enter absolute temperature
Provide temperature in Kelvin to match the gas constant units.
Review osmotic pressure
The calculator reports osmotic pressure in both atm and kPa for convenience.
Formula
pi = i M R T
pi is osmotic pressure, M molarity, i van't Hoff factor, R the gas constant, T absolute temperature.
Example
For M = 0.2 mol/L, i = 2, T = 298 K: pi = 2 * 0.2 * 0.082057366 * 298 about 9.8 atm.
Full Description
Osmotic pressure quantifies the tendency of solvent to flow across a semipermeable membrane to equalize solute concentrations.
The van't Hoff relation mirrors the ideal gas law assumption and works well for dilute solutions of electrolytes or nonelectrolytes.
Frequently Asked Questions
Does concentration need to be molarity?
Yes. Convert molality or mass fraction to molarity before using the formula.
How do I handle non-ideal solutions?
Use osmotic coefficients or activity-based models when concentrations are high or ions interact strongly.
Can I input Celsius temperatures?
Convert Celsius to Kelvin by adding 273.15 before entering the value.
Why include van't Hoff factor?
Electrolytes dissociate into multiple particles, increasing osmotic pressure in proportion to i.
Is the gas constant value important?
Yes. Ensure R is consistent with the units used for molarity and temperature. The preset constant outputs atm when molarity is in mol/L.