Dog Free Water Deficit Calculator
Calculate free water deficit in hypernatraemic dogs and guide safe correction rate.
What Is the Dog Free Water Deficit Calculator?
Calculate free water deficit in hypernatraemic dogs and guide safe correction rate.
Rapid correction of hypernatraemia causes cerebral oedema. This calculator quantifies the deficit and provides safe correction rate guidance.
Every result is based on published veterinary research and breed-size-specific growth data — not generic averages. This tool is completely free, works instantly in your browser, and requires no account or sign-up.
How to Use This Calculator
Fill in the required fields above — typically your dog's weight, age, or breed size. Every field has a clear label and hint.
Press the calculate button to get your instant result. No page reload, no account needed, no waiting.
Your result appears immediately below the calculator. It includes the primary answer plus additional context where relevant.
Share, print, or save your result. Always discuss health-related results with your veterinarian before making decisions.
How It Works
Free water deficit occurs when sodium concentration rises above normal (hypernatraemia) due to relative water loss exceeding solute loss. The body retains sodium but loses free water — through panting, fever, diabetes insipidus, or inadequate water intake. The free water deficit quantifies how much pure water (not saline) must be replaced to normalise sodium. Formula: Free Water Deficit (L) = TBW × ((Measured Na ÷ Target Na) − 1) where TBW (Total Body Water) = 0.6 × body weight in kg. Correction must be gradual — dropping serum sodium faster than 10–12 mEq/L per 24 hours risks cerebral oedema.
Normal serum sodium in dogs: 140–155 mEq/L. Target for correction: 145 mEq/L.
Sources: DiBartola SP. Disorders of sodium and water. In: DiBartola SP ed. Fluid, Electrolyte and Acid-Base Disorders in Small Animal Practice 2012; Burkitt Creedon JM. Sodium disorders in critically ill patients. Vet Clin North Am Small Anim Pract 2013.
Veterinary Research
Every formula is derived from peer-reviewed veterinary studies and clinical guidelines, not guesswork or generic rules.
Instant Results
No page reload, no waiting, no account needed. Enter your details and your result appears immediately.
100% Private
All calculations happen in your browser. Nothing you enter is ever stored on our servers or shared with anyone.
Always Free
Every calculator on Doggy Calculators is and will always be completely free to use — no premium tier, no catch.
FAQ
Sources & References
This calculator's formulas are based on the following peer-reviewed and authoritative veterinary sources:
- Merck Veterinary Manual u2014 Clinical Reference — Clinical formulas, normal reference ranges, and diagnostic criteria
- WSAVA Guidelines for Veterinary Practice — International veterinary clinical standards
- Ettinger's Textbook of Veterinary Internal Medicine — Advanced clinical reference for fluid therapy, haematology, and diagnostics
- RECOVER Initiative u2014 CPR Guidelines — Emergency drug dosing and resuscitation protocols
⚠️ These calculators are reference tools only. Always consult a licensed veterinarian before administering medication or making medical decisions.