Oxygen Consumption Rate Calculator

Reviewed by the CalculatorHub team, edited by James Graham. Fick principle. Last verified 15 June 2026.

The Fick principle calculates whole-body oxygen consumption (VO2) as the product of cardiac output and the arteriovenous oxygen content difference: VO2 (mL/min) = cardiac output (L/min) x (CaO2 - CvO2) (mL/dL) x 10. The factor of 10 converts the oxygen content difference from mL per dL to mL per litre. Enter cardiac output, arterial oxygen content (CaO2), and mixed venous oxygen content (CvO2) to obtain VO2 in mL/min and the indexed value in mL/min/m2 if BSA is provided. This is a research and clinical education tool; patient care decisions require validated clinical measurement.

Cardiac output (L/min) Normal resting: 4-8 L/min. Measured by thermodilution or Doppler.

Arterial O2 content CaO2 (mL/dL) Normal: 18-21 mL/dL. Compute as: Hgb x 1.34 x SaO2 + PaO2 x 0.0031.

Mixed venous O2 content CvO2 (mL/dL) Normal: 13-16 mL/dL. From pulmonary artery (mixed venous) sample.

BSA (m2, optional, for VO2 index) Leave as 1.73 if unknown (standard reference BSA).

VO2 (mL/min)

250.00

VO2 index (mL/min/m2)

144.51

A-V O2 difference (mL/dL)

5.00

Fick principle formula

VO2 (mL/min) = CO (L/min) x (CaO2 - CvO2) (mL/dL) x 10
VO2 index = VO2 / BSA (m2)
A-V O2 difference = CaO2 - CvO2

The factor 10 converts cardiac output from per litre to per decilitre (10 dL per litre) to match the O2 content units.

Normal reference values

VO2 at rest: 200-250 mL/min (approximately 3.5 mL/kg/min).
VO2 index: approximately 110-160 mL/min/m2.
Cardiac output: 4-8 L/min; cardiac index: 2.2-4.0 L/min/m2.
CaO2: 18-21 mL/dL; CvO2: 13-16 mL/dL.
Arteriovenous oxygen difference: 4-6 mL/dL at rest.

Frequently asked questions

What is the Fick principle?

The Fick principle states that the rate of oxygen consumption by the body equals the product of cardiac output and the arteriovenous oxygen content difference: VO2 = CO x (CaO2 - CvO2). It was derived by Adolf Fick in 1870 and is the gold standard for measuring cardiac output and oxygen consumption.

What are CaO2 and CvO2?

CaO2 is the arterial oxygen content (oxygen carried per decilitre of arterial blood) and CvO2 is the mixed venous oxygen content. CaO2 is measured from arterial blood (typically radial artery); CvO2 from a pulmonary artery catheter sample (mixed venous). Both are in mL O2 per dL blood.

How is oxygen content (CaO2) calculated?

CaO2 (mL/dL) = (Hgb x 1.34 x SaO2) + (PaO2 x 0.0031). The first term is oxygen bound to haemoglobin; 1.34 is the O2-carrying capacity of haemoglobin (mL O2/g Hgb); the second term is dissolved oxygen (usually small). Normal CaO2 is approximately 18-20 mL/dL.

What is normal VO2?

Normal resting VO2 for an adult is approximately 200-250 mL/min, or about 3.5 mL/kg/min (= 1 MET). During maximal exercise, VO2max can reach 35-80 mL/kg/min depending on fitness level. Critically ill patients often have elevated VO2 due to increased metabolic demand.

What is oxygen extraction ratio?

Oxygen extraction ratio (O2ER) = (CaO2 - CvO2) / CaO2 x 100%. It represents the fraction of delivered oxygen that is consumed by tissues. Normal O2ER is approximately 22-30%. Values above 50-60% suggest inadequate oxygen delivery (DO2) relative to demand.

Official sources

NIH/NCBI: Fick Principle and cardiac output measurement.
NCBI Bookshelf: Oxygen delivery and consumption physiology.

Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.