💧 Osmotic Pressure Calculator (π = iMRT)
Enter the molarity, temperature and van't Hoff factor to get the osmotic pressure π = iMRT, shown in atm, kPa and mmHg.
Osmotic pressure (π = iMRT)
2.4465 atm
= 247.9 kPa · 1859.4 mmHg · at 298.15 K
Osmotic pressure is the pressure needed to stop solvent flowing across a semipermeable membrane into a solution: π = iMRT, with R = 0.08206 L·atm/(mol·K) and T in kelvin. The van't Hoff factor i counts the particles each formula unit releases (1 for glucose, 2 for NaCl). 🔒 In your browser.
How the osmotic pressure calculator (π = imrt) works
Osmotic pressure is the pressure that must be applied to a solution to stop pure solvent flowing into it across a semipermeable membrane: π = i·M·R·T, where i is the van't Hoff factor (particles per formula unit), M the molarity (mol/L), R the gas constant 0.08206 L·atm/(mol·K), and T the absolute temperature in kelvin. The tool converts your Celsius temperature to kelvin and reports the pressure in atmospheres, kilopascals and millimetres of mercury.
The van't Hoff factor counts the dissolved particles: 1 for a non-electrolyte like glucose, 2 for NaCl or KCl (which split into two ions), 3 for CaCl₂. Osmotic pressure is a colligative property — it depends on the number of dissolved particles, not their identity — which is why it can be used to measure the molar mass of large molecules like proteins.
Frequently asked questions
What is osmotic pressure?
The pressure needed to stop solvent moving by osmosis into a solution through a semipermeable membrane. It rises with how many solute particles are dissolved, making it a colligative property.
How do you calculate osmotic pressure?
π = iMRT, where i is the van't Hoff factor, M the molarity in mol/L, R = 0.08206 L·atm/(mol·K) and T the temperature in kelvin. A 0.1 M glucose solution at 25 °C gives about 2.45 atm.
What is the van't Hoff factor?
The number of particles a formula unit produces in solution: 1 for glucose (stays whole), 2 for NaCl (Na⁺ + Cl⁻), 3 for CaCl₂ (Ca²⁺ + 2Cl⁻). It multiplies the effective concentration of particles.
Why does NaCl give twice the osmotic pressure of glucose?
Because each NaCl unit dissociates into two ions (i = 2) while glucose stays as one particle (i = 1). Colligative properties count particles, so the same molarity of NaCl exerts about double the osmotic pressure.
Why does temperature matter?
Osmotic pressure is proportional to absolute temperature (T in kelvin) — warmer solutions push harder, just as with gas pressure. Always convert °C to K by adding 273.15; the tool does this automatically.