By Zencalcy Editorial TeamLast reviewed About us
The Fick principle states that the oxygen a person consumes equals the cardiac output multiplied by the difference in oxygen content between arterial and venous blood. Rearranging it gives cardiac output from three measurements. This calculator applies that rearrangement and reports flow in litres per minute.
Cardiac output from oxygen consumption and content difference.
CO (L/min) = VO2 (mL/min) ÷ (CaO2 − CvO2) ÷ 10
The oxygen contents are in mL O2 per dL, so dividing by 10 converts the result from dL to litres. The arterial content must exceed the venous content for the calculation to make sense. A typical resting cardiac output is around 4–8 L/min, but it varies with body size and metabolic demand.
| Symbol | Meaning |
|---|---|
| VO2 | Oxygen consumption in millilitres per minute. |
| CaO2 | Arterial oxygen content in mL O2 per dL. |
| CvO2 | Venous oxygen content in mL O2 per dL. |
| CO | Cardiac output in litres per minute. |
The arteriovenous difference is 20 − 15 = 5 mL/dL. Cardiac output = 250 ÷ 5 ÷ 10 = 5.00 L/min. With VO2 240 mL/min and a difference of 19 − 14 = 5 mL/dL, the result is 240 ÷ 5 ÷ 10 = 4.80 L/min.
The principle is a mass balance. Oxygen enters the blood in the lungs and leaves it in the tissues, and the amount consumed per minute must equal the flow multiplied by the difference in content across the circulation. That makes the calculation elegant but sensitive to measurement error, because a small error in the arteriovenous difference produces a large error in flow. The method also assumes steady-state conditions, so a rapidly changing patient may not fit the model. In practice, content values are calculated from haemoglobin, saturation and dissolved oxygen rather than measured directly. That adds steps where error can enter. Despite these limits, the Fick approach remains a reference method and a useful way to understand why cardiac output depends on both oxygen demand and the ability of blood to carry and deliver oxygen.
Continue with the Mean Arterial Pressure Calculator, Pulse Pressure Calculator, or the QTc Calculator — or browse more cardiology tools and all health calculators.
Oxygen content is expressed per decilitre, while cardiac output is expressed per litre. One litre contains ten decilitres, so dividing by ten converts the units. Without that step the number would be ten times too large.
Blood pressure, ECG and risk scores are screening aids, not diagnoses. A single reading can be misleading; trends and proper technique matter. Scores estimate population risk and do not replace clinical assessment, anticoagulation decisions or emergency care.
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Last reviewed: September 2026. See how we build and check every tool on the about page.
Content updated: September 2026