⚗️ Lab Calculators
Osmolarity Calculator
Calculate total osmolarity of solutions with multiple solutes. Add any number of components, set their dissociation factors, and get total mOsm/L with isotonicity classification.
How to Use the Osmolarity Calculator
Add each solute in your solution by entering its name, concentration in mM, and its dissociation factor (number of particles it produces per formula unit). Click Calculate Osmolarity to get the total mOsm/L with a breakdown per solute and an isotonicity classification.
Osmolarity Formula
Osmolarity (mOsm/L) = Σ [Concentration (mM) × i]
where i = number of osmotic particles per formula unit
i = 1 for non-electrolytes (glucose, urea, sucrose) | i = 2 for NaCl, KCl, MgCl₂ type | i = 3 for CaCl₂, Na₂SO₄ type
Common i-factors (Dissociation Particles)
i = 1 (Non-electrolytes)
Glucose, sucrose, urea, mannitol, sorbitol, most organic molecules. Do not dissociate in water.
i = 2 (1:1 electrolytes)
NaCl → Na⁺ + Cl⁻, KCl → K⁺ + Cl⁻, NaHCO₃, NaOH. Each molecule gives 2 particles.
i = 3 (1:2 electrolytes)
CaCl₂ → Ca²⁺ + 2Cl⁻, Na₂SO₄ → 2Na⁺ + SO₄²⁻, MgCl₂. Each molecule gives 3 particles.
Physiological range
Human blood plasma: 275–295 mOsm/L. Isotonic cell culture media: 280–320 mOsm/L. Normal saline: ~308 mOsm/L.
About Osmolarity in Biotechnology
Osmolarity measures the total concentration of osmotically active solute particles in a solution. It determines whether cells will swell (hypotonic solution) or shrink (hypertonic solution) when placed in the solution, making it critical for cell culture, tissue preparation and drug formulation.
The osmolarity of cell culture media must be carefully controlled — most mammalian cells require 280–320 mOsm/L for optimal growth and viability. Significant deviation from this range causes osmotic stress and reduces experimental reproducibility.
🔵 Hypotonic (< 275 mOsm/L)
Cells swell and may lyse. Used intentionally for cell lysis in some extraction protocols (hypotonic lysis buffer).
🟢 Isotonic (275–295 mOsm/L)
Cells maintain normal volume. Required for cell culture, blood-compatible infusions and physiological experiments.
🔴 Hypertonic (> 295 mOsm/L)
Cells shrink and may crenate. Mild hypertonic conditions (<400 mOsm/L) can improve recombinant protein production in CHO cells.
📋 Osmolarity vs Osmolality
Osmolarity = mOsm per litre of solution. Osmolality = mOsm per kg of solvent (water). In dilute aqueous solutions, the two are nearly equal.
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