Cardiac Index Calculator

Estimate cardiac output, body surface area, and cardiac index from heart rate, stroke volume, height, and weight, with standard reference ranges.

Quick Facts

Cardiac output
CO = HR × SV
Heart rate (beats/min) times stroke volume (mL/beat), converted to L/min.
Body surface area (Mosteller)
BSA = √(height(cm) × weight(kg) / 3600)
A widely used estimate of total body surface area in m².
Cardiac index
CI = CO / BSA
Normal resting range is about 2.5-4.0 L/min/m².
Educational tool
Not a diagnosis
Real cardiac output is usually measured directly by a clinician, not estimated from these inputs alone.

Your Results

Calculated
Cardiac Index
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CI = CO / BSA, in L/min/m²
Cardiac Output
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CO = HR × SV, in L/min
Body Surface Area
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Mosteller formula, in m²
Category
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Compared to the 2.5-4.0 L/min/m² normal range

Ready

Enter heart rate, stroke volume, height, and weight, then press Calculate.

Formula and Method for the Cardiac Index Calculator

Cardiac index (CI) is cardiac output normalized to body size, so people of different sizes can be compared on the same scale. It is calculated in two steps: first, cardiac output (CO) is found from heart rate and stroke volume — CO = HR × SV — then CO is divided by body surface area (BSA) to get CI = CO / BSA, expressed in liters per minute per square meter (L/min/m²). This calculator estimates BSA using the Mosteller formula, BSA = √(height(cm) × weight(kg) / 3600), one of the most widely used BSA equations in clinical medicine.

How the calculation works

Enter heart rate in beats per minute and stroke volume — the amount of blood the heart pumps per beat, typically around 60-100 mL at rest — in milliliters. Multiplying these gives cardiac output in mL/min, which the calculator converts to L/min. Enter height and weight (in either metric or imperial units) to compute body surface area with the Mosteller formula. Dividing cardiac output by BSA yields the cardiac index.

Interpreting cardiac index values

A normal resting cardiac index generally falls between 2.5 and 4.0 L/min/m². A cardiac index below about 2.2 L/min/m² is a threshold clinicians associate with cardiogenic shock when seen alongside signs of poor organ perfusion. A cardiac index above 4.0 L/min/m² can reflect a hyperdynamic circulatory state, seen in conditions such as fever, sepsis, anemia, hyperthyroidism, or pregnancy.

Limitations and clinical context

This calculator is an educational tool, not a diagnostic device. In real clinical settings, cardiac output is usually measured directly — via thermodilution through a pulmonary artery catheter, echocardiography, or pulse contour analysis — rather than derived from an assumed stroke volume. Heart rate and stroke volume both vary with activity, medications, hydration, and underlying heart or lung disease, so a single estimate should never replace evaluation by a qualified healthcare provider. If you or someone else has symptoms of low cardiac output (dizziness, low blood pressure, cold extremities, confusion), seek medical care rather than relying on a calculator.

Frequently Asked Questions

What is cardiac index and how is it calculated?
Cardiac index (CI) is cardiac output normalized to body size: CI = CO / BSA, measured in L/min/m². Cardiac output (CO) equals heart rate times stroke volume, and body surface area (BSA) is commonly estimated with the Mosteller formula: BSA = √(height(cm) × weight(kg) / 3600).
What is a normal cardiac index range?
A normal resting cardiac index is generally 2.5 to 4.0 L/min/m². Values below about 2.2 L/min/m² are associated with cardiogenic shock in the right clinical context, while values above 4.0 L/min/m² can reflect a hyperdynamic state such as sepsis, fever, anemia, or pregnancy.
Why does cardiac index use body surface area instead of cardiac output alone?
Cardiac output naturally varies with body size, since a larger person needs more blood flow than a smaller person even with an equally healthy heart. Dividing cardiac output by body surface area normalizes for this difference, which makes cardiac index more comparable across people of different sizes.
Is this calculator a substitute for a clinical cardiac output measurement?
No. In clinical practice, cardiac output is usually measured directly with methods such as thermodilution, echocardiography, or pulse contour analysis rather than estimated from heart rate and stroke volume alone. This calculator is an educational tool for understanding the relationship between these variables and is not a substitute for professional medical evaluation.

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