Fluid Therapy Calculator

Maintenance + dehydration replacement + ongoing losses, summed and converted to mL/hr. Pick a class to apply species-appropriate maintenance constants — mammals, birds, and reptiles each have their own published baselines.

Species class

Adult dog: 40–60 mL/kg/day; puppies/lactating: up to 80.

Body weight

Maintenance rate (mL/kg/day)

Dehydration (%)

Ongoing losses (mL/day)

Replace deficit over (hours)

How the math works

Maintenance: mammal default 60 mL/kg/day (cat) or 80 mL/kg/day (dog/exotic mammal); avian 50 mL/kg/day; reptile 25 mL/kg/day. These are standard published rates and conservative for healthy patients — adjust upward for high-output critical cases.
Dehydration replacement: % dehydration × body weight (kg) × 1000 = mL deficit. Most references replace this volume over 12–24 hours alongside maintenance, NOT as a bolus. Severe (≥10%) cases need slower correction with frequent re-assessment.
Ongoing losses: estimate from vomit/diarrhoea volume, polyuria, drains, third- spacing. Add separately to maintenance + replacement.
Total daily volume = maintenance + replacement + ongoing losses. Divide by 24 for mL/hr.

Reference only — not veterinary advice. Adjust for cardiac / renal compromise, third-spacing, and individual response. See our avian fluid therapy article or reptile fluids guidance for species-specific deep-dives.