Animal Body Surface Area Calculator
Body surface area (BSA) is used to dose certain veterinary drugs, especially some chemotherapy agents, because surface area tracks metabolic rate more closely than weight alone. The standard formula gives BSA in square metres as K times body weight in grams to the power two-thirds, divided by 10,000, where K is a species constant (about 10.1 for dogs and 10.0 for cats). Enter the animal's weight, choose the unit, and set K from your dosing protocol. The tool computes surface area only; the actual drug and dose must come from a veterinarian. Never use this to self-dose an animal.
10.1 for dogs, about 10.0 for cats (use your protocol value).
Body surface area formula
Weight (g) = weight (kg) * 1000
BSA (m squared) = K * (weight in grams ^ (2/3)) / 10000
K is the species constant. The two-thirds exponent reflects the geometric scaling of surface area with body mass. Convert pounds to kilograms first (divide by 2.2046226) if needed.
Surface-area dosing context
- BSA dosing is used for specific drug classes, notably some chemotherapy agents.
- K is commonly 10.1 for dogs and about 10.0 for cats; sources vary slightly.
- Most veterinary drugs are still dosed per kilogram of body weight.
- Surface area tracks metabolic rate better than weight across very different sizes.
- The drug, dose, and dosing basis must always come from a veterinarian.
Body surface area: frequently asked questions
How is animal body surface area calculated?
The standard veterinary formula is body surface area in square metres equals K times body weight in grams to the power two-thirds, divided by 10,000. K is a species constant, commonly 10.1 for dogs and about 10.0 for cats. The two-thirds exponent reflects how surface area scales with mass.
Why is body surface area used in veterinary medicine?
Some drugs, particularly certain chemotherapy agents, are dosed per square metre of body surface area rather than per kilogram. This is because surface area tracks metabolic rate more closely than weight alone, especially across very different body sizes. The dose must always come from a veterinary protocol.
What value of K should I use?
K is 10.1 for dogs in the most widely cited reference and approximately 10.0 for cats. Because sources differ slightly, K is an editable input here. Use the constant specified in the dosing protocol you are following.
Does body surface area replace weight-based dosing?
No. Most veterinary medicines are still dosed per kilogram. Surface-area dosing is used for specific drug classes where it is clinically validated. Always follow the dosing basis stated in the drug's label or your veterinarian's protocol.
Is this a substitute for veterinary calculation?
No. This is an educational tool to compute surface area from weight. The actual dose, drug, and dosing basis must be set and checked by a veterinarian. Never use this to self-dose an animal.
Official sources
- Merck Veterinary Manual: Veterinary pharmacology and dosing.
- U.S. FDA Center for Veterinary Medicine: Animal & Veterinary.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.