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. The normal cardiac index runs about 2.5 to 4 L/min/m².1 This calculator uses 2.2 to 4.0 as its normal band. Values below it may point to heart failure or cardiogenic shock, and values above it to 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 works out your cardiac index. 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.3
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.1
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.
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). The normal cardiac index runs about 2.5 to 4 L/min/m², and a value under 2 raises suspicion of cardiogenic shock.1 This calculator uses 2.2 to 4.0 as its normal band. Either way, the index catches heart problems that raw cardiac output alone can 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.
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.
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. Cardiogenic shock is defined as below 2.2 L/min/m² with circulatory support, or below 1.8 without it.1 The heart is not pumping enough blood to meet the body's basic needs.
- 1.8 to 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.
- 2.2 to 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.
This calculator is meant for educational purposes only. Always rely on a qualified healthcare provider to interpret cardiac index values and make treatment decisions.