Clinical judgment required. This calculator is a decision-support tool, not a substitute for veterinary consultation.

Serum Osmolality CalculatorCanineFeline

Calculate estimated serum osmolality from sodium, BUN, and glucose in dogs and cats. Uses the standard formula: 2(Na) + BUN/2.8 + Glucose/18. Normal range: 290–310 mOsm/kg in dogs, 290–330 mOsm/kg in cats. Elevated osmolality (hyperosmolar state) may indicate hypernatremia, diabetic hyperosmolar syndrome, ethylene glycol toxicity, or severe dehydration. The osmolal gap (measured − calculated, normal < 10) helps detect unmeasured osmoles such as toxins. Used for dehydration assessment, DKA monitoring, toxicology workup (ethylene glycol, methanol), hyperglycemic hyperosmolar syndrome evaluation, and fluid therapy planning. Common queries: 'serum osmolality formula', 'calculated osmolarity dog', 'osmolal gap calculation', 'hyperosmolar state assessment'.

Species

Sodium (Na⁺)

mEq/L

BUN

mg/dL

Glucose

mg/dL

Estimated Osmolality

—mOsm/kg

280 mOsm/kg

310 mOsm/kg

340 mOsm/kg

Low

Moderate

High