About Osmolar

Osmolar is an independent reference for osmolarity and osmolality across the whole chain: blood, bag and bottle. It brings together calculators, worked examples and cited data tables in one place, for anyone who needs to understand or check these numbers.

What we cover

• Blood: calculated serum osmolality, the osmolal gap, effective osmolality, sodium correction in hyperglycemia, free water deficit, and serum and urine reference ranges.
• Bag: the osmolarity of IV fluids and parenteral nutrition, including the 900 mOsm/L figure commonly used for peripheral PN and why institutional thresholds vary.
• Bottle: enteral formulas and the medicines given with them, oral rehydration solutions and sports drinks.
• Learning: osmolality versus osmolarity, tonicity, how osmometers work, and practice problems with full worked answers.

Who it is for

Osmolar is written for nursing, medical, pharmacy and dietetics students; for pharmacists, dietitians, nurses and doctors who want to check a calculation; for laboratory staff; and for readers trying to understand a test result. Pages written for patients explain what a result means. They do not give treatment advice.

Why we built it

Calculators for serum osmolality are easy to find, but many show a single formula with little explanation. Tools for the osmolarity of the things people are given or drink, such as IV admixtures, parenteral nutrition, enteral feeds and rehydration drinks, are scattered across older web pages, PDFs and tables in papers. Osmolar aims to put these in one modern, readable place, with each formula shown and each number traceable to its source.

How we work

Every page follows the same rules:

• Show the working. Each calculator shows its formula (in both US and SI units where they differ), defines every input, states how results are rounded, and names the alternatives where sources disagree. At least one worked example on each calculator page matches a reference test case.
• Cite every number. Ranges, factors, thresholds and product values come from clinical guidelines, official product labels, primary studies or established references. Each one is cited with a link. Calculated and measured values are labelled as such.
• Test the calculators. Each formula is checked against a set of reference test cases with known answers, written as automated unit tests.
• Check before publishing. Each page goes through a separate Medical QA check, and each calculator must pass all of its automated test cases. No clinician reviews our pages, and every medical page says so. “Last checked” and “Last updated” dates appear on the page.
• Correct openly. Pages are re-checked at least every 12 months, and as soon as practical when we learn that a cited source, guideline or label has changed. Significant corrections are dated on the page.

Pages, calculator code and data tables are drafted with AI tools, and the Medical QA check is also carried out with AI tools against a written, sourced reference. No clinician has reviewed the content. Pages publish automatically under publishing rules set by the site owner once they pass Medical QA review and automated tests.

The full process, including our source hierarchy, corrections policy and how to report an error, is on the How we check content page.

Privacy

The calculators run in your browser. What you type is not stored or sent anywhere. Osmolar sets no tracking or advertising cookies. Our host, Cloudflare, may set a strictly necessary security cookie (e.g. cf_clearance). We use Cloudflare Web Analytics, which Cloudflare describes as cookieless, to count page views in aggregate and measure page speed. A consent banner will appear before any non-essential cookies, Google Analytics (GA4) or ads are ever added. Details are on the Disclaimer page.

Independence and money

Osmolar is free to use, independent and not sponsored. We may earn affiliate commissions, disclosed on the page, from exam-preparation courses (nursing, pharmacy and medical), textbooks and books, and adult sports and electrolyte brands (not oral rehydration solutions marketed for illness, and nothing for infants or children). We do not use affiliate links for osmometers or other laboratory equipment, and any future sponsorship will carry its own disclosure. At launch the site has no ads.

Commercial relationships do not shape medical content. Partners have no say over formulas, numbers, ranges, product comparisons or QA outcomes. Affiliate links are disclosed on the page, kept in separate, labelled boxes, never on calculator pages or inside data or comparison tables, and left off patient-facing pages. Our full policy is in the affiliate disclosure.

Educational use

Osmolar is an educational reference, not medical advice. Results are estimates and calculation aids, not dosing or treatment decisions. Check any result against your institution’s protocols and with the responsible pharmacist or clinician. In an emergency, call your local emergency number. See the Disclaimer.

Who publishes Osmolar

Osmolar is published by Osmolar. The site has no named authors, editors or clinical reviewer. Pages are drafted with AI tools and checked as described above. See How we check content.

Contact

hello@osmolar.com

To report an error in our content, see How to report an error on the How we check content page. We cannot give advice about individual patients or test results.