Pet Blood Volume Calculator
Circulating blood volume in dogs and cats is estimated from body weight using a species factor in mL per kilogram. This calculator takes the weight, the blood-volume factor (which you set for the species and animal), and a safe-sampling percentage, and returns the estimated total blood volume and the safe sampling or donation volume. Every clinical value is a user-editable input: the tool performs arithmetic only and is not a substitute for veterinary judgement.
Blood volume formula
Total blood volume (mL) = weight (kg) * factor (mL/kg)
Safe sampling volume (mL) = total * (percent / 100)
The factor is the species blood-volume coefficient you supply. The sampling fraction is the percentage of total volume your veterinarian considers safe for the patient.
Worked example
A 20 kg dog at 90 mL/kg with a 10 percent sampling limit: total = 20 * 90 = 1,800.00 mL. Safe sampling volume = 1,800 * 0.10 = 180.00 mL.
Pet blood volume: frequently asked questions
How much blood does a dog or cat have?
Total blood volume is estimated from body weight using a species factor in mL per kilogram. Commonly cited factors are about 80 to 90 mL/kg for dogs and about 50 to 66 mL/kg for cats. The exact value varies with age and body condition, so it is entered as a user-editable input here.
What is a safe blood sampling volume?
A common guideline limits a single sample to a small fraction of total blood volume in a healthy animal. This calculator lets you enter that fraction as a percentage and applies it to the estimated total. Always follow your veterinarian's limit for the individual patient and its health status.
Is this a clinical decision tool?
No. Blood collection and transfusion decisions must be made by a veterinarian. This calculator is an arithmetic aid that multiplies body weight by a factor you supply and applies a percentage you supply.
Official sources
- U.S. Food and Drug Administration: Animal and Veterinary.
- The total-volume and sampling relationships follow from the definitions of volume per unit mass and percentage of a total.
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.