Serum Osmolality Calculator
Calculated osmolality and the osmolar gap — the toxic-alcohol screen hiding in routine chemistry.
Sodium (doubled for its anions) dominates normal osmolality — 275–295 is the usual band. The gap is the pearl: a measured value >10 above calculated means something osmotically active the formula doesn't know about, classically methanol or ethylene glycol in the right story (add ethanol/3.7 if ethanol is on board). Time-critical when it matters.
Formula
Reference aid for healthcare professionals only. Every result must be independently verified before clinical use. Never use this tool for self-medication or to replace clinical judgement.
Calculated osmolality and the osmolar gap — the toxic-alcohol screen hiding in routine chemistry. The Serum Osmolality Calculator is a free, private serum osmolality tool — every result computes instantly in your browser with no sign-up and no data upload.
About Serum Osmolality Calculator
Sodium (doubled for its anions) dominates normal osmolality — 275–295 is the usual band. It applies Osm = 2×Na + glucose/18 + BUN/2.8; gap = measured − calculated. Use the Serum Osmolality Calculator to get an instant, clearly-explained result with the working shown step by step — free, private and with the source method cited.
How to use Serum Osmolality Calculator
- 1Enter your details in the Serum Osmolality Calculator input fields above.
- 2The result updates instantly with the working and reference bands shown.
- 3Adjust any value to explore how it changes the outcome — it's free and unlimited.
Why use Serum Osmolality Calculator?
- ✓Instant serum osmolality result that recomputes as you type — no waiting, no page reloads
- ✓100% client-side: your health data never leaves your browser
- ✓Shows the actual formula and your numbers substituted in, so you can see exactly how the result is reached
- ✓Based on published, citable sources (Purssell RA et al., Ann Emerg Med 2001 — osmolar gap in toxicology)
- ✓Free forever with no sign-up, account or app install
Frequently asked questions
How does the Serum Osmolality Calculator work?+
Sodium (doubled for its anions) dominates normal osmolality — 275–295 is the usual band. The calculation uses the formula: Osm = 2×Na + glucose/18 + BUN/2.8; gap = measured − calculated. Everything runs instantly in your browser as you type — your inputs are never uploaded.
Is the Serum Osmolality Calculator accurate, and what is it based on?+
The method is traceable to authoritative sources: Purssell RA et al., Ann Emerg Med 2001 — osmolar gap in toxicology. Results are estimates — individual variation always applies, so treat the output as a well-grounded starting point.
Is the Serum Osmolality Calculator free and private?+
Yes. It's completely free with no sign-up, and all computation happens locally in your browser, so none of your health data ever leaves your device.
Can I use this for medical decisions?+
This is a reference aid for healthcare professionals and must be independently verified. It is not for self-diagnosis or self-medication.
What can I use the Serum Osmolality Calculator for?+
It's commonly used for serum osmolality, osmolar gap, calculated osmolality. Calculated osmolality and the osmolar gap — the toxic-alcohol screen hiding in routine chemistry.
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