Osmolarity Calculator Formula

Understand the math behind the osmolarity calculator. Each variable explained with a worked example.

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Formulas Used

Osmolarity

osmolarity = molarity * vant_hoff

Milliosmolarity

milliosmolarity = molarity * vant_hoff * 1000

Variables

VariableDescriptionDefault
molarityMolarity(M)0.15
vant_hoffVan't Hoff Factor (i)2

How It Works

How to Calculate Osmolarity

Formula

Osmolarity = M × i

Where:

  • M = molarity
  • i = van't Hoff factor (particles per formula unit)

    • For NaCl, i = 2. For glucose, i = 1.

    Worked Example

    Osmolarity of 0.15 M NaCl (i = 2).

    molarity = 0.15vant_hoff = 2
    1. 01Osmolarity = M × i
    2. 02Osmolarity = 0.15 × 2
    3. 03Osmolarity = 0.3 Osm/L = 300 mOsm/L

    Frequently Asked Questions

    What is osmolarity?

    Total concentration of all solute particles in a solution, measured in osmoles per liter. It determines osmotic pressure.

    What is the van't Hoff factor?

    The number of particles a solute dissociates into. NaCl: i=2, CaCl2: i=3, glucose: i=1.

    What is normal blood osmolarity?

    Normal blood osmolarity is 275-295 mOsm/L.

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