Osmolality Calculator
Calculate serum osmolality, effective osmolality (tonicity), and osmolar gap for metabolic evaluation and toxic ingestion workup.
Lab Values
mEq/L
Normal: 135-145 mEq/L
mOsm/kg
For osmolar gap calculation
mg/dL
To account for alcohol contribution
Calculated Osmolality
291 mOsm/kg
Normal
🧪Calculated Osm
291 mOsm/kg
💧Effective Osm
286 mOsm/kg
📊Osmolar Gap
-0.9 mOsm/kg
Osmolar Gap: Normal
Normal osmolar gap (-10 to +10 mOsm/kg)
Osmolality Formulas
Calculations
Osm = 2 × Na + (Glucose/18) + (BUN/2.8)
Effective Osm = 2 × Na + (Glucose/18)
Osmolar Gap = Measured - Calculated
Causes of Elevated Gap
- Methanol poisoning
- Ethylene glycol poisoning
- Isopropyl alcohol
- Mannitol administration
- Contrast agents
- Severe ketoacidosis