Osmotic Pressure Calculator

What osmotic pressure means

Osmotic pressure is the pressure required to stop net solvent flow across an ideal semipermeable membrane separating a solution from pure solvent. In dilute solution it behaves mathematically like a gas-law analogue, because the effect scales with the number of dissolved particles.

That is why the page reports both formal molarity and particle molarity i × M. Higher temperature or more dissolved particles produces a larger osmotic pressure under the same ideal assumptions.

Formula used here

This calculator uses the van't Hoff relation Π = iMRT. M is molarity in mol/L, T is absolute temperature in kelvin, R is the gas constant in L·atm·mol^-1·K^-1, and i is the van't Hoff factor.

Worked example

A 0.15 M sodium chloride solution at 25 °C with i ≈ 1.9 gives an osmotic pressure of about 7.0 to 7.4 atm under the ideal-dilute model, depending on rounding. The calculator then converts that value into kPa, bar, torr, mmHg, or psi as needed.

Because the equation depends on kelvin temperature, the page can also reverse-solve the temperature or effective van't Hoff factor when the other quantities are known.