pharmcal: Osmolarity Calculator

Osmolarity Calculator (Osm/L) | PharmCal Professional Suite

Osmolarity Calculator

Calculate Molar Osmolarity (Osm/L) for Isotonicity

Mass of Solute

Molecular Weight (MW)

g/mol

Volume of Solution

Number of Particles (n)

Molarity: 0 M

Osmolarity: 0 Osm/L

Milliosmolarity: 0 mOsm/L

Tonicity Estimate: Waiting...

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Understanding Osmolarity in Pharmacy

Osmolarity is a measure of the solute particle concentration per liter of solution. It is a critical parameter for intravenous (IV) fluids, ophthalmic solutions, and parenteral nutrition to prevent tissue damage (lysis or shrinkage) caused by osmotic pressure differences.

Step 1: Determine Solute Properties

Identify the Molecular Weight (MW) and the Dissociation Factor (n).
Examples:
- Dextrose: n=1 (does not dissociate).
- NaCl: n=2 (dissociates into Na+ and Cl-).
- CaCl₂: n=3 (dissociates into Ca²+ and 2Cl-).

Step 2: Input Mass and Volume

Enter the mass of the solute used and the total final volume of the solution.

Calculation Formula

Osmolarity = Molarity × n

= ( Mass(g) / MW ) / Volume(L) × n

Result is typically expressed in mOsm/L (milliosmoles per liter).

Tonicity Reference Guide

Isotonic: ~270 to 300 mOsm/L (e.g., 0.9% Normal Saline). Compatible with blood.
Hypotonic: < 270 mOsm/L. Causes cells to swell.
Hypertonic: > 300 mOsm/L. Causes cells to shrink. High osmolarity fluids must be administered via central lines.

Labels: Osmolarity Calculator