Osmotic Pressure Calculator. Osmotic pressure is the force a solution exerts to draw water across a semipermeable membrane — a critical concept in biology, medicine, and chemistry. Enter your solution's molarity, van't Hoff factor (how many particles the solute splits into when dissolved), and temperature into the Osmotic Pressure Calculator to get the osmotic pressure in atm, with secondary outputs in kPa and mmHg. Also try the use the Vapor Pressure Calculator.
Osmotic pressure is the minimum pressure that must be applied to a solution to prevent the flow of solvent through a semi-permeable membrane. It's the pressure required to completely stop osmosis. See also our TDS Calculator (Total Dissolved Solids).
The van't Hoff factor (i) represents the number of particles a solute forms when it dissolves. For non-electrolytes like glucose, i ≈ 1. For NaCl, i ≈ 2. For CaCl₂, i ≈ 3. Real values may be lower due to ion pairing.
The van't Hoff equation is used: Π = i × M × R × T, where Π is osmotic pressure, i is the van't Hoff factor, M is molarity, R is the gas constant (0.082057 L·atm·mol⁻¹·K⁻¹), and T is absolute temperature.
Osmotic pressure is crucial for understanding biological processes, designing reverse osmosis systems, and predicting solution behavior. It helps determine the operational pressure needed for water treatment systems.
Osmotic pressure increases linearly with temperature. Higher temperatures result in higher osmotic pressure because molecular motion increases, leading to greater tendency for osmosis to occur.
The calculator provides osmotic pressure in atmospheres (atm), kilopascals (kPa), and millimeters of mercury (mmHg) for convenience in different applications and scientific contexts. You might also find our calculate Mass Concentration to Molar Concentration Converter Converted Concentration useful.