Volume of Distribution Calculator
Volume of distribution (Vd) is the hypothetical volume that relates the total amount of drug in the body to the observed plasma concentration. For a simple one-compartment model after an IV bolus, Vd = Dose / C0, where C0 is the initial plasma concentration (extrapolated to time zero from the elimination phase). Vd is expressed in litres and often normalized by body weight (L/kg). It determines the loading dose required to achieve a target plasma concentration and explains why some drugs have concentrations that decline very slowly (large Vd, extensive tissue distribution).
Volume of distribution formula
Vd (L) = Dose (mg) / C0 (mg/L)
Vd (L/kg) = Vd (L) / Weight (kg)
C0 is the theoretical initial concentration after IV bolus (time zero extrapolation). In practice, C0 is estimated by back-extrapolating the log-linear elimination phase to time zero using multiple plasma samples.
Interpreting Vd values
- Vd approximately 3 to 5 L (0.04 to 0.07 L/kg): drug confined mainly to plasma (e.g., heparin, large protein molecules).
- Vd approximately 10 to 20 L (0.14 to 0.28 L/kg): distribution into extracellular fluid (e.g., warfarin, some antibiotics).
- Vd approximately 40 to 50 L (0.5 to 0.7 L/kg): total body water distribution (e.g., ethanol, some beta-blockers).
- Vd greater than 50 L (more than 0.7 L/kg): extensive tissue binding (e.g., digoxin 7 L/kg, chloroquine up to 800 L/kg).
Volume of distribution: frequently asked questions
What is volume of distribution?
Volume of distribution (Vd) is a hypothetical volume that would be required to contain the total amount of drug in the body at the same concentration as observed in plasma. It is a proportionality constant, not an actual anatomical volume. Units are typically L or L/kg.
What does a large Vd indicate?
A large Vd (e.g., greater than 10 L/kg) indicates extensive distribution into tissues, with relatively little drug in the plasma. Drugs such as chloroquine (Vd approximately 250 to 800 L/kg) and digoxin (Vd approximately 7 L/kg) have very large Vd values due to high tissue binding.
What does a small Vd indicate?
A small Vd (close to plasma volume, approximately 0.04 to 0.07 L/kg) indicates the drug is largely confined to the vascular compartment. Warfarin (Vd approximately 0.14 L/kg) and heparin have relatively small Vd values due to high plasma protein binding.
How does Vd relate to half-life and clearance?
t1/2 = 0.693 x Vd / CL. A drug with large Vd and low clearance will have a very long half-life. Understanding Vd is essential for calculating loading doses: LD = Vd x target Cp / F.
Can this calculator be used for clinical patient care?
This tool is for educational and pharmacokinetic learning purposes only. Clinical Vd estimation requires multiple plasma samples, appropriate pharmacokinetic modeling, and professional interpretation within patient-specific context.
Official sources
- U.S. Food and Drug Administration: FDA Pharmacokinetics Guidance.
- NIH National Library of Medicine: Pharmacokinetics (StatPearls).
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.