Cardiac Output Calculator

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Walk-through

How to Use This Calculator

4 steps

1

Choose SV × HR or the Fick method

Use the SV × HR tab when you already know stroke volume (from echocardiography or another measurement) and heart rate — the direct definition of cardiac output. Use the Fick Method tab when you instead have oxygen consumption and an arterial/venous blood-gas sample, which is common during right-heart catheterization when stroke volume isn't measured directly.

2

Enter your values

SV × HR needs stroke volume in mL and heart rate in bpm. The Fick method needs oxygen consumption (VO2) in mL/min, arterial O2 content (CaO2), and mixed venous O2 content (CvO2), both in mL O2 per dL of blood. Both tabs update instantly as you type.

3

Read the result and its band

The headline shows cardiac output in L/min, with a colour-coded classification: Critically low, Low, Normal (4–8 L/min), Elevated, or High. The interpretation line spells out whether the value falls inside the normal range.

4

Check the Normal Range tab

Open the Normal Range tab for the full reference table — your most recent result from either method is highlighted — plus context on cardiac index, exercise effects, and shock states. Use Share or Copy to save a reading; your numbers are encoded in the URL.

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Reference

Formula & Methodology

2 formulas

Cardiac output — SV × HR

CO (L/min) = SV (mL) × HR (bpm) ÷ 1000

The direct definition of cardiac output: the volume of blood ejected per beat (stroke volume) times the number of beats per minute (heart rate), converted from mL/min to L/min.

Cardiac output — Fick method

CO (L/min) = VO2 (mL/min) ÷ [(CaO2 − CvO2) (mL O2/dL) × 10]

The Fick principle: oxygen consumption divided by the arteriovenous oxygen content difference. Arterial and venous O2 content are conventionally measured per 100 mL (dL) of blood, so the ×10 in the denominator converts that per-dL difference to a per-litre basis, returning CO directly in L/min. Example: VO2 250 mL/min, CaO2 20, CvO2 15 → CO = 250 ÷ (5 × 10) = 5 L/min.

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YMYL

Trust, Methodology & Sources

Reviewed by Calculover Editorial Review · Updated 2026-07-22 · 3 sources

Editorial accountability

Author: Calculover Editorial Team - Editor

Owner: Calculover Editorial Team - Editorial owner

Reviewer: Calculover Editorial Review - Medical-source review

Last reviewed: 2026-07-22

Last verified: 2026-07-22

Data effective: 2026-07-22

Methodology

The Cardiac Output Calculator applies two standard hemodynamic formulas. SV × HR: CO = stroke volume (mL) × heart rate (bpm) ÷ 1000, the direct definition of cardiac output. Fick method: CO = oxygen consumption VO2 (mL/min) ÷ [(arterial O2 content CaO2 − venous O2 content CvO2) (mL O2/dL) × 10], the Fick principle applied to oxygen transport, with the ×10 factor converting the per-decilitre oxygen content difference to a per-litre basis. Interpretation bands (< 4 below typical resting range, 4–8 typical resting range, 8–10 above typical resting range, > 10 markedly elevated L/min) are broad adult reference ranges, not patient-specific diagnostic thresholds.

Assumption: Stroke volume, heart rate, oxygen consumption, and O2 content values are entered for the same patient at the same point in time.

Assumption: The Fick method requires arterial O2 content to exceed venous O2 content (a positive arteriovenous difference); a zero or negative difference cannot be resolved into a valid flow rate.

Assumption: The user wants a screening estimate and interpretation context, not a diagnosis, treatment plan, or dosing decision.

Limitations & guidance

SV × HR and the Fick method rely on the accuracy of their respective inputs (echocardiographic stroke volume, or measured VO2 and blood-gas oxygen content) — this calculator performs the arithmetic only and cannot validate the underlying measurements.

Interpretation bands are general adult reference ranges; actual targets vary by patient size, condition, and care setting, and clinicians typically prefer cardiac index (CO normalized to body surface area) over raw CO for cross-patient comparison.

This tool does not diagnose, monitor, or guide treatment of any condition. Do not make medical decisions based on its output.

Professional guidance: The Cardiac Output Calculator is for health education and clinical decision support only. It provides an estimate based on user-entered values, not medical advice, diagnosis, treatment, or a substitute for direct hemodynamic monitoring or care from a licensed healthcare professional. Always rely on a qualified clinician for medical decisions.

Primary sources

Vincent JL. Understanding cardiac output. Critical Care. - Critical Care (BioMed Central)

Kosinski S, Darocha T, et al. The Fick principle and its clinical application. Anaesthesiology Intensive Therapy. - Anaesthesiology Intensive Therapy

Hall JE. Guyton and Hall Textbook of Medical Physiology — Cardiac Output, Venous Return, and Their Regulation. - Elsevier

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Glossary

Key Terms Explained

7 terms

Cardiac output (CO) The volume of blood the heart pumps per minute, in litres per minute (L/min). Normal resting adult CO is roughly 4–8 L/min.

Stroke volume (SV) The volume of blood ejected by the left ventricle with each heartbeat, in millilitres (mL). Typical resting adult value: 60–100 mL.

Fick principle A method for calculating blood flow (here, cardiac output) from the rate a substance is taken up or released (here, oxygen) divided by the difference in that substance's concentration across the circulation.

Arteriovenous oxygen difference (avDO2) The difference between arterial and mixed venous oxygen content (CaO2 − CvO2), reflecting how much oxygen tissues extract from the blood as it circulates. A normal resting value is roughly 4–5 mL O2/dL.

Hemodynamics The study of blood flow and the forces (pressure, resistance, flow) that govern it within the cardiovascular system.

VO2 (oxygen consumption) The rate at which the body consumes oxygen, in mL/min. Resting adult VO2 is roughly 200–300 mL/min and rises substantially with exercise.

Cardiac index (CI) Cardiac output divided by body surface area (CO ÷ BSA), expressed in L/min/m². It normalizes CO for body size, making it more comparable across different-sized patients than raw CO.

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Scenarios

Real-World Examples

3 worked examples

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Resting adult — echocardiogram

SV × HR method, 70 mL × 75 bpm

Stroke volume 70 mL Heart rate 75 bpm Cardiac output 5.25 L/min

CO = 70 × 75 ÷ 1000 = 5.25 L/min, comfortably inside the normal 4–8 L/min range for a resting adult. This is the textbook baseline most references cite for stroke volume and heart rate at rest.

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Right-heart catheterization — Fick method

VO2 250 mL/min, CaO2 20, CvO2 15

Oxygen consumption (VO2) 250 mL/min Arterial O2 content (CaO2) 20 mL O2/dL Venous O2 content (CvO2) 15 mL O2/dL Cardiac output 5 L/min

Arteriovenous O2 difference is 20 − 15 = 5 mL O2/dL. CO = 250 ÷ (5 × 10) = 5 L/min — the classic textbook Fick example, and it lands right alongside the SV × HR method's 5.25 L/min for a similar resting patient, as it should.

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Low-output warning sign

SV × HR method, 35 mL × 55 bpm

Stroke volume 35 mL Heart rate 55 bpm Cardiac output 1.93 L/min

CO = 35 × 55 ÷ 1000 = 1.93 L/min — below a broad adult reference range. Cardiac output alone cannot diagnose shock; urgent clinical evaluation is appropriate when low output is accompanied by concerning symptoms or signs of poor perfusion.

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Deep Dive

Understanding Cardiac Output

3 chapters · 5 min read

Cardiac output is the single number that captures how much blood the heart delivers to the body each minute — the product of how much it ejects per beat and how often it beats. This guide explains the two standard ways to calculate it, why they should agree, what a normal range looks like, and where each method's assumptions can lead you astray.

Two routes to the same number

Cardiac output (CO) can be measured or estimated in more than one way, and this calculator offers the two most common. The direct route is CO = SV × HR: multiply stroke volume (blood ejected per beat, from echocardiography or another direct measurement) by heart rate. The indirect route is the Fick method, CO = VO2 ÷ [(CaO2 − CvO2) × 10], which derives flow from how much oxygen the body consumes and how much oxygen content drops as blood passes through the tissues.

The Fick method matters clinically because stroke volume isn't always directly measured — during right-heart catheterization, for example, clinicians often have oxygen consumption and blood-gas samples on hand instead. For the same patient at the same moment, both methods should return very similar cardiac output values; a substantial disagreement is a signal to recheck the inputs, most often the oxygen content values in the Fick calculation.

Why the ×10 factor in the Fick equation

Arterial and venous oxygen content (CaO2, CvO2) are conventionally reported per 100 mL, or one decilitre (dL), of blood — a legacy of how blood-gas values are conventionally expressed. Oxygen consumption (VO2), by contrast, is reported per minute in millilitres, with no decilitre normalization. Dividing VO2 directly by the oxygen content difference would give a flow rate in dL/min, not L/min, so the equation multiplies the denominator by 10 (or equivalently divides the whole ratio by 10) to convert deciliters to litres. It's a unit-conversion step, not part of the underlying physiology.

Reading the result against a normal range

A typical resting adult cardiac output is roughly 4–8 L/min, though it scales with body size — which is why clinicians often prefer cardiac index (CO divided by body surface area) when comparing across patients. CO rises substantially during exercise as both stroke volume and heart rate increase, so a single resting measurement only tells part of the story.

Very low output can be concerning, but cardiac output alone cannot diagnose cardiogenic shock. Clinicians also consider blood pressure, cardiac index, filling pressures, lactate, urine output, mental status, and other signs of perfusion. Sepsis, severe anemia, thyrotoxicosis, and arteriovenous fistulas can alter cardiac output above the typical resting range. This calculator is educational and does not replace direct hemodynamic monitoring or clinical judgment.

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Questions

Frequently Asked Questions

6 questions

What is a normal cardiac output?+

A typical resting adult cardiac output is roughly 4–8 L/min. It scales with body size, so clinicians often use cardiac index (CO divided by body surface area, in L/min/m²) to compare across patients of different sizes. Cardiac output rises substantially during exercise.

How does the Fick method compare to thermodilution?+

The Fick method calculates cardiac output from oxygen consumption and the arteriovenous oxygen difference — useful when stroke volume isn't measured directly, such as during right-heart catheterization. Thermodilution, the other common invasive method, injects a small volume of cold saline and measures the temperature change downstream to derive flow. Both are established clinical techniques; the Fick method is often considered more reliable at low flow states, while thermodilution is faster to repeat at the bedside.

What units does this calculator use?+

Cardiac output is reported in litres per minute (L/min). Stroke volume is in millilitres (mL), heart rate in beats per minute (bpm), oxygen consumption (VO2) in mL/min, and arterial/venous oxygen content (CaO2, CvO2) in millilitres of O2 per decilitre of blood (mL O2/dL).

What are the signs of low cardiac output?+

Symptoms can include fatigue, shortness of breath, cold extremities, low blood pressure, rapid or weak pulse, and confusion or lightheadedness as organ perfusion falls. A low calculated output is not a diagnosis; urgent clinical evaluation is appropriate when concerning symptoms or signs of poor perfusion are present.

How is cardiac output related to cardiac index?+

Cardiac index is cardiac output divided by body surface area (CI = CO ÷ BSA), expressed in L/min/m². Because a larger person normally has a higher absolute cardiac output, cardiac index gives a size-normalized value that's more comparable across different patients — useful when judging whether a given CO is adequate for that specific person.

How does heart rate affect cardiac output?+

Cardiac output is the direct product of stroke volume and heart rate, so increasing heart rate raises CO as long as stroke volume holds steady — which is exactly what happens during moderate exercise. At very high heart rates, though, the heart has less time to fill between beats, which can reduce stroke volume enough to blunt or even reverse the expected rise in cardiac output.

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Stroke Volume & Heart Rate

Cardiac Output

Fick Principle

Cardiac Output (Fick)

Cardiac Output Reference Bands

Reading CO in Context

Optional body-size context

How to Use This Calculator

Choose SV × HR or the Fick method

Enter your values

Read the result and its band

Check the Normal Range tab

Formula & Methodology

Trust, Methodology & Sources

Key Terms Explained

Real-World Examples

Resting adult — echocardiogram

Right-heart catheterization — Fick method

Low-output warning sign

Understanding Cardiac Output

Two routes to the same number

Why the ×10 factor in the Fick equation

Reading the result against a normal range

Frequently Asked Questions

Get a branded PDF of your results

❤️ Stroke Volume & Heart Rate

📊 Cardiac Output

🫁 Fick Principle

📊 Cardiac Output (Fick)

📈 Cardiac Output Reference Bands

🩺 Reading CO in Context

Optional body-size context

How to Use This Calculator

Choose SV × HR or the Fick method

Enter your values

Read the result and its band

Check the Normal Range tab

Formula & Methodology

Trust, Methodology & Sources

Key Terms Explained

Real-World Examples

Understanding Cardiac Output

Two routes to the same number

Why the ×10 factor in the Fick equation

Reading the result against a normal range

Frequently Asked Questions

Get a branded PDF of your results

Keep Exploring

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Guides & articles

Stroke Volume & Heart Rate

Cardiac Output

Fick Principle

Cardiac Output (Fick)

Cardiac Output Reference Bands

Reading CO in Context