Osmotic Pressure Calculator (π = iMRT)
Enter molarity, the van ‘t Hoff factor and temperature to get osmotic pressure.
Your numbers
Your results
Osmotic pressure (atm)
Osmotic pressure (atm)
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Osmotic pressure (bar)
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Osmotic pressure (kPa)
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Osmolarity (osmol/L)
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Osmotic Pressure Calculator (π = iMRT) by TheCalcTools
How the Osmotic Pressure Calculator (π = iMRT) works
Osmotic pressure is the pressure needed to stop water flowing across a semipermeable membrane into a solution. For dilute solutions it follows the van ‘t Hoff equation π = iMRT.
Physiological saline (about 0.15 M NaCl) has an osmolarity near 0.3 osmol/L, matching body fluids.
The formula
π = i × M × R × T, R = 0.082057366 L·atm/(mol·K)
Worked example
Using the default values shown in the calculator:
| Molarity (mol/L) | 0.15 |
|---|---|
| Van 't Hoff factor i | 2 |
| Temperature (°C) | 37 |
- 0.15 M NaCl at 37 °C: π = 2 × 0.15 × 0.08206 × 310.15 = 7.64 atm (774 kPa).
Result:
| Osmotic pressure (atm) | 7.635 |
|---|---|
| Osmotic pressure (bar) | 7.736 |
| Osmotic pressure (kPa) | 773.6 |
| Osmolarity (osmol/L) | 0.300 |
Frequently asked questions
Why does seawater dehydrate you?
Its osmolarity (about 1 osmol/L) is much higher than blood’s, so water would move out of your cells.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.