Cardiac Index Calculator

Q: What is a normal Cardiac Index value?

A normal Cardiac Index is between 2.2 and 4.0 L/min/m² . This means your heart is pumping enough blood for your body size at rest.

Q: What inputs do I need for this calculator?

You need two things: Cardiac Output and Body Surface Area . For Cardiac Output, you can enter heart rate and stroke volume, or type in a known CO value. For BSA, you can enter your height and weight, or type in a known BSA value.

Q: What is the difference between Cardiac Output and Cardiac Index?

Cardiac Output (CO) is the total blood your heart pumps per minute in liters. Cardiac Index (CI) divides that number by your body surface area. CI adjusts for body size, so it is a fairer way to judge heart function across people of different sizes.

Q: What do the colors on the gauge mean?

Red means critically low (below 1.8). Orange means low, in the cardiogenic shock range (1.8 to 2.2). Green means normal (2.2 to 4.0). Blue means elevated, which may suggest a high-output state (above 4.0).

Q: What does a Cardiac Index below 1.8 mean?

A CI below 1.8 L/min/m² is critically low . It means your heart is not pumping enough blood to meet your body's basic needs. This level is linked to organ damage and high mortality risk. It requires urgent medical attention.

Q: What does an elevated Cardiac Index above 4.0 mean?

A CI above 4.0 L/min/m² is considered elevated . It does not always mean your heart is stronger. It can be caused by conditions like sepsis, severe anemia, hyperthyroidism, or an arteriovenous fistula. A doctor should evaluate the cause.

Cardiac Index Calculator

Updated Jul 18, 2026 By Jehan Wadia

Introduction

The Cardiac Index (CI) tells doctors how well your heart pumps blood based on your body size. It is one of the most useful numbers in cardiology because it accounts for whether a person is small or large. A normal Cardiac Index falls between 2.2 and 4.0 L/min/m². Values below this range may point to heart failure or cardiogenic shock, while values above it may signal a high-output state like sepsis.

To find the Cardiac Index, you divide Cardiac Output (the total blood your heart pumps each minute) by Body Surface Area (a measure of your body's outer size in square meters). The formula is simple: CI = CO ÷ BSA.

This Cardiac Index Calculator does the math for you in seconds. You can enter heart rate and stroke volume to derive Cardiac Output, or type it in directly. For Body Surface Area, you can enter your height and weight and let the tool estimate it using the Mosteller or Haycock formula, or enter a known BSA value. The calculator then shows your result on a color-coded gauge, gives a clinical interpretation, and walks you through each step of the math.

How to Use Our Cardiac Index Calculator

This calculator needs your heart's output and your body size to find your Cardiac Index (CI). It will show your CI in L/min/m², tell you if it is normal, and give you a step-by-step breakdown of the math.

Choose how to enter Cardiac Output (CO). You can pick "Derive from HR × SV" to let the tool figure it out from your heart rate and stroke volume, or pick "Enter CO directly" if you already know your cardiac output in liters per minute.

Heart Rate (HR). If you chose to derive CO, type your heart rate in beats per minute. A normal resting heart rate is 60 to 100 beats per minute. If you are unsure about your heart rate zones or want to find your maximum heart rate, you can use dedicated tools designed for that purpose.

Stroke Volume (SV). Type the amount of blood your heart pumps with each beat in milliliters. A normal value is 60 to 100 mL per beat.

Cardiac Output (CO) — direct entry. If you chose the direct option, type your known cardiac output in liters per minute. A normal range is 4.0 to 8.0 L/min.

Choose how to enter Body Surface Area (BSA). You can pick "Estimate from height & weight" to have the tool calculate it, or pick "Enter BSA directly" if you already know it. If you need to calculate BSA on its own, our BSA Calculator provides a dedicated tool for that.

Height. If you chose to estimate BSA, type your height. Use the dropdown next to the field to switch between centimeters (cm) and inches (in).

Weight. Type your weight. Use the dropdown to switch between kilograms (kg) and pounds (lbs).

BSA Formula. Pick which formula the tool uses to estimate your body surface area. Mosteller is the default and most common. You can also check "Compare both formulas" to see results from both Mosteller and Haycock side by side.

Body Surface Area (BSA) — direct entry. If you chose the direct option, type your known BSA in square meters (m²). A normal adult range is 1.5 to 2.0 m².

Display Options. Use the checkboxes to show or hide the gauge, step-by-step solution, physiology note, and perfusion note. You can also change the rounding mode between clinical (2 decimal places) and full precision.

Quick Picks. If you want to test the tool or see a sample case, click any preset button at the top. It will fill in all fields and calculate instantly.

Calculate. Press the blue "Calculate" button to see your Cardiac Index result, clinical interpretation, and visual gauge. Press "Reset" to clear all fields and start over.

What Is Cardiac Index?

Cardiac index (CI) is a number that tells doctors how well your heart pumps blood based on your body size. It is measured in liters per minute per square meter (L/min/m²). A normal cardiac index falls between 2.2 and 4.0 L/min/m². This number helps doctors spot heart problems that raw cardiac output alone might miss.

How Is Cardiac Index Calculated?

The cardiac index formula is simple:

Cardiac Index = Cardiac Output ÷ Body Surface Area

Cardiac output (CO) is the total amount of blood your heart pumps each minute. You can find it by multiplying your heart rate (beats per minute) by your stroke volume (the amount of blood pushed out with each heartbeat). The result is then divided by 1,000 to convert from milliliters to liters. If you want to understand how your heart rate relates to exercise intensity, our Heart Rate Zone Calculator and Target Heart Rate Calculator can help.

Body surface area (BSA) is an estimate of the total area of your skin, measured in square meters (m²). It is calculated from your height and weight. Two common formulas used to estimate BSA are the Mosteller formula and the Haycock formula. Both give very similar results in most adults. You can also use our BSA Calculator to compute this value independently. For other body-size metrics, tools like the BMI Calculator and Ideal Body Weight Calculator offer additional perspectives.

Why Does Cardiac Index Matter?

Two people can have the same cardiac output, but if one person is much larger, their body needs more blood flow. Cardiac index adjusts for body size, so it gives a fairer picture of how well the heart is working. This makes it more useful than cardiac output alone when comparing patients or tracking changes over time. When used alongside other hemodynamic markers such as mean arterial pressure, cardiac index provides a more complete view of cardiovascular function.

What Do the Results Mean?

Below 1.8 L/min/m² — Critically low. The heart is not pumping enough blood to meet the body's basic needs. This level is linked to a high risk of organ damage. Monitoring kidney function with tools like the GFR Calculator can help assess end-organ perfusion in these cases.
1.8 – 2.2 L/min/m² — Low. This range is often seen in cardiogenic shock, a dangerous condition where the heart suddenly cannot pump enough blood. Clinicians may also evaluate IV infusion rates and vasopressor dosing to support circulation at this level.
2.2 – 4.0 L/min/m² — Normal. The heart is pumping the right amount of blood for the body's size at rest.
Above 4.0 L/min/m² — Elevated. This may point to a high-output state caused by conditions like sepsis, severe anemia, or an overactive thyroid.

When Is Cardiac Index Used?

Doctors measure cardiac index most often in intensive care units and during heart catheterization procedures. It helps guide treatment in patients with heart failure, shock, or severe infections. It is also used before and after heart surgery to check how well the heart recovers. Alongside cardiac index, clinicians often assess cardiovascular risk using tools such as the ASCVD Risk Calculator, Framingham Risk Calculator, and CHA2DS2-VASc Calculator. Other related cardiac measurements, like the QTc interval and cholesterol ratio, round out a comprehensive cardiac evaluation. For athletes or fitness-minded individuals, the VO2 Max Calculator offers insight into cardiovascular fitness and oxygen utilization capacity.

This calculator is meant for educational purposes only. Always rely on a qualified healthcare provider to interpret cardiac index values and make treatment decisions.

Formulas used

Cardiac Index

CI = \frac{CO}{BSA}

Cardiac Output from Heart Rate and Stroke Volume

CO = \frac{HR \times SV}{1000}

BSA — Mosteller Formula

BSA = \sqrt{\frac{h \times w}{3600}}

BSA — Haycock Formula

BSA = 0.024265 \times h^{0.3964} \times w^{0.5378}

Frequently asked questions

What is a normal Cardiac Index value?

A normal Cardiac Index is between 2.2 and 4.0 L/min/m². This means your heart is pumping enough blood for your body size at rest.

What inputs do I need for this calculator?

You need two things: Cardiac Output and Body Surface Area. For Cardiac Output, you can enter heart rate and stroke volume, or type in a known CO value. For BSA, you can enter your height and weight, or type in a known BSA value.

What is the difference between Cardiac Output and Cardiac Index?

Cardiac Output (CO) is the total blood your heart pumps per minute in liters. Cardiac Index (CI) divides that number by your body surface area. CI adjusts for body size, so it is a fairer way to judge heart function across people of different sizes.

What is stroke volume and where do I get it?

Stroke volume (SV) is the amount of blood your heart pushes out with each beat, measured in milliliters. It is usually measured by an echocardiogram or a pulmonary artery catheter. A normal value is 60 to 100 mL per beat.

What is the difference between the Mosteller and Haycock BSA formulas?

Both formulas estimate your body surface area from height and weight. Mosteller is simpler and most commonly used in adults. Haycock is often preferred in pediatric settings. In most adults, both give very close results. You can check "Compare both formulas" to see the difference.

Can I switch between metric and imperial units?

Yes. Use the dropdown next to the height field to switch between centimeters and inches. Use the dropdown next to the weight field to switch between kilograms and pounds. The calculator will convert your entered value automatically when you switch.

What do the colors on the gauge mean?

Red means critically low (below 1.8). Orange means low, in the cardiogenic shock range (1.8 to 2.2). Green means normal (2.2 to 4.0). Blue means elevated, which may suggest a high-output state (above 4.0).

What does a Cardiac Index below 1.8 mean?

A CI below 1.8 L/min/m² is critically low. It means your heart is not pumping enough blood to meet your body's basic needs. This level is linked to organ damage and high mortality risk. It requires urgent medical attention.

What does an elevated Cardiac Index above 4.0 mean?

A CI above 4.0 L/min/m² is considered elevated. It does not always mean your heart is stronger. It can be caused by conditions like sepsis, severe anemia, hyperthyroidism, or an arteriovenous fistula. A doctor should evaluate the cause.

What are the Quick Pick presets?

Quick Picks are sample scenarios that fill in all the inputs for you. They include a Resting Adult, an Athletic / High Output case, a Low Output / Shock case, and a Critically Low case. They are useful for learning how the calculator works or comparing different clinical situations.

Does this calculator work for children?

The calculator can compute a Cardiac Index for any valid height and weight, but the normal CI ranges shown are based on adult values. Children may have different normal ranges. Always consult a pediatric cardiologist for interpreting CI in children.

Why does my derived Cardiac Output show a warning?

If the heart rate multiplied by stroke volume gives a Cardiac Output below 2.0 L/min, the calculator shows a warning. This is a critically low level that is rarely seen in stable patients. It asks you to double-check your heart rate and stroke volume entries for errors.

What does the step-by-step solution show?

It walks you through every math step the calculator performed. This includes the CI formula, how CO was derived from HR and SV, how BSA was estimated from height and weight, any unit conversions, and the final division that gives you the Cardiac Index.

Can I enter Cardiac Output and BSA directly without using heart rate or height?

Yes. Select "Enter CO directly" under Cardiac Output and "Enter BSA directly" under Body Surface Area. Then type your known CO in L/min and BSA in m². The calculator will divide them to find your CI.

What is the difference between clinical rounding and full precision?

Clinical rounding shows results to 2 decimal places, which is standard in medical practice. Full precision shows more decimal places for academic or research use. You can switch between them in the Display Options section.

Is this calculator a substitute for medical advice?

No. This tool is for educational purposes only. Cardiac Index values must be interpreted by a qualified healthcare provider who can consider your full medical history, physical exam, and other test results before making treatment decisions.

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