Osmolarity Converter
Convert between Osm/L, mOsm/L, mOsm/kg, mmol/L, and more
Conversion Formula:
Multiply by 1
Common Conversions
Note: Conversions between mOsm/L, mmol/L, and mEq/L assume monovalent ions (e.g., Na+, K+, Cl-). For divalent ions (e.g., Ca2+, Mg2+), the relationship varies based on ion valence.
Understanding Osmolarity
Osmolarity is the measure of solute concentration, defined as the number of osmoles (osm) of solute per liter of solution. It's used in chemistry, biology, and medicine to describe the concentration of osmotically active particles in a solution.
Osmolality is related but measures osmoles per kilogram of solvent rather than per liter of solution. For dilute aqueous solutions, osmolarity and osmolality values are very close (within about 0.5%).
Key Terms:
- Osmole (Osm): Unit of osmotic pressure, equal to 1 mole of osmotically active particles.
- Tonicity: Effective osmotic pressure gradient between two solutions across a semipermeable membrane.
- Isotonic: Solutions with the same effective osmotic pressure as body fluids (~290 mOsm/L).
- Hypotonic: Solutions with lower effective osmotic pressure than body fluids.
- Hypertonic: Solutions with higher effective osmotic pressure than body fluids.
Clinical Applications
| Solution | Osmolarity | Clinical Use |
|---|---|---|
| D5W (5% Dextrose in Water) | 252 mOsm/L | Hypotonic fluid for hydration |
| 0.45% NaCl (1/2 Normal Saline) | 154 mOsm/L | Hypotonic fluid replacement |
| 0.9% NaCl (Normal Saline) | 308 mOsm/L | Isotonic fluid replacement |
| Lactated Ringer's | 273 mOsm/L | Balanced electrolyte solution |
| 3% NaCl (Hypertonic Saline) | 1026 mOsm/L | Treatment of severe hyponatremia |
| 20% Mannitol | 1098 mOsm/L | Reduction of intracranial pressure |
Cellular Response to Osmolarity
Hypotonic Environment
When cells are placed in a hypotonic solution (< 275 mOsm/L), water moves into the cells causing them to swell. In extreme cases, this can lead to cell lysis.
Isotonic Environment
In isotonic solutions (275-295 mOsm/L), there is no net movement of water, and cells maintain their normal volume. This is the ideal environment for most cells.
Hypertonic Environment
In hypertonic solutions (> 295 mOsm/L), water moves out of cells causing them to shrink (crenation). This can impair cellular function.
Calculating Osmolarity
Osmolarity can be calculated or estimated using the following formula:
Plasma Osmolarity (mOsm/L) = 2[Na+] + [Glucose]/18 + [BUN]/2.8
Where: [Na+] is in mmol/L, [Glucose] and [BUN] are in mg/dL
For IV fluids and other solutions, osmolarity is calculated from the composition:
- Electrolytes contribute based on their dissociation in solution
- 1 mole of NaCl dissociates into 2 osmoles (Na+ and Cl-)
- Non-electrolytes (like glucose) generally contribute 1 osmole per mole
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Visual Comparison
290.00 mOsm/L
Normal (Isotonic)
Similar to: Blood Plasma
Normal human blood plasma
Clinical Effects
In isotonic solutions, there is no net water movement across cell membranes, maintaining normal cell volume.
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About the Osmolarity Converter
Convert between Osm/L, mOsm/L, mOsm/kg, mmol/L, and more All conversions run instantly in your browser and nothing you enter is sent to a server.
Common Conversion Formulas
| From | To | Formula |
|---|---|---|
| Osmoles per liter (Osm/L) | Milliosmoles per liter (mOsm/L) | mOsm/L = Osm/L × 1000 |
| Milliosmoles per liter (mOsm/L) | Milliosmoles per kilogram (mOsm/kg) | mOsm/kg ≈ mOsm/L × 0.995 |
| Milliosmoles per liter (mOsm/L) | Milliequivalents per liter (mEq/L) | mEq/L = mOsm/L × Valence (for monovalent ions) |