Pet Dehydration Deficit

About this calculator

A pet’s fluid deficit from dehydration is estimated as: deficit (mL) = body weight (kg) x % dehydration x 1000, plus ongoing maintenance and losses on top. A 10 kg dog assessed at 8% dehydrated has an estimated 800 mL fluid deficit that needs replacing, independent of its normal daily fluid needs.

Veterinarians estimate dehydration percentage from clinical signs — skin tent time, gum moisture and capillary refill, sunken eyes — since there’s no direct way to measure fluid loss in an animal, then use that percentage to calculate how much replacement fluid (given IV or subcutaneously) is needed, typically over 4-24 hours depending on severity. Getting this number right matters because under-replacing prolongs recovery while over-replacing too quickly risks fluid overload, especially in small or cardiac-compromised patients.

This calculator takes a pet’s body weight and estimated dehydration percentage and returns the fluid deficit in milliliters that needs to be replaced.