Osmotic Pressure Calculator
Calculate osmotic pressure with π = iMRT, solve for molarity or the van't Hoff factor, and convert the result to atm, bar and pascals.
What this calculator does
Enter the molarity, temperature and van't Hoff factor and get the osmotic pressure in atm, bar and Pa, or rearrange to find the molarity or i.
When you need it
Osmotic pressure matters in biology and engineering, from how cells keep their shape to reverse osmosis water treatment and the measurement of polymer molar masses.
Formulas
- π = i · M · R · T
- R = 0.08206 L·atm/(mol·K)
- 1 atm = 1.01325 bar = 101 325 Pa
How to use it
- Choose to find π, the molarity or i.
- Enter the other values with the temperature in kelvin.
- Read the pressure in atm, bar and Pa.
Worked example
Find the osmotic pressure of 0.10 M glucose at 25 °C.
- T = 25 + 273.15 = 298.15 K, and i = 1 for glucose
- π = 1 × 0.10 mol/L × 0.08206 L·atm/(mol·K) × 298.15 K
- π = 2.45 atm
Answer
The osmotic pressure is 2.45 atm.
Common mistakes
- Using °C for the temperature.
- Forgetting the van't Hoff factor for ionic solutes.
- Using molality instead of molarity.
Related tools
Frequently asked questions
What is osmotic pressure?
The pressure that has to be applied to a solution to stop solvent flowing into it through a semipermeable membrane.
Why is it written like the ideal gas law?
For dilute solutions, π = MRT has the same form as PV = nRT, because the solute particles behave like gas particles.
How is osmotic pressure used?
It is used to find the molar mass of large molecules such as polymers and proteins.