Cardiac Index Calculator
Calculate cardiac index (CI) from cardiac output (CO) and body surface area (BSA).
CI units: L/min/m²
If you don't know BSA, estimate it below using height and weight.
Estimate BSA (Mosteller Formula)
What is cardiac index?
Cardiac index is a hemodynamic value that adjusts cardiac output for body size. While cardiac output tells you how much blood the heart pumps per minute, cardiac index gives a more individualized measure by dividing that output by body surface area. This helps clinicians compare heart performance across people with different body builds.
Cardiac index formula
The formula is straightforward:
- Cardiac Index (L/min/m²) = Cardiac Output (L/min) ÷ Body Surface Area (m²)
If your cardiac output is measured in mL/min, convert it to L/min first by dividing by 1000.
How to use this cardiac index calculator
Step 1: Enter cardiac output
Input your cardiac output and choose the correct unit (L/min or mL/min).
Step 2: Enter or estimate BSA
If you already know BSA, enter it directly. If not, use height and weight and click Estimate BSA. This calculator uses the Mosteller method:
- BSA (m²) = √[(Height in cm × Weight in kg) / 3600]
Step 3: Calculate
Click Calculate Cardiac Index to see your result and a quick interpretation.
Typical interpretation ranges
Exact ranges can vary slightly by institution and clinical context, but these are commonly used reference points:
- Below 2.2 L/min/m²: Low (may suggest reduced perfusion)
- 2.2 to 2.5 L/min/m²: Borderline low
- 2.5 to 4.0 L/min/m²: Typical adult resting range
- Above 4.0 L/min/m²: High output state
Example calculation
Suppose a patient has:
- Cardiac Output: 5.0 L/min
- BSA: 1.8 m²
Cardiac Index = 5.0 ÷ 1.8 = 2.78 L/min/m², which falls in a commonly accepted normal resting range.
Why cardiac index matters clinically
Cardiac index is used in critical care, cardiology, and perioperative medicine to evaluate circulatory performance. It is especially useful when blood pressure alone doesn't tell the full story of tissue perfusion.
- Assessment of shock states (e.g., cardiogenic, septic)
- Guidance for vasoactive medication and fluid management
- Monitoring advanced heart failure
- Support for hemodynamic decision-making in ICU settings
Important limitations
- Cardiac index is one data point and must be interpreted with symptoms, blood pressure, lactate, urine output, and exam findings.
- BSA formulas are estimates and may not perfectly fit all body compositions.
- Measured cardiac output methods (thermodilution, echocardiography, etc.) can produce different values.
Quick FAQ
Is cardiac index the same as ejection fraction?
No. Ejection fraction is the percentage of blood ejected from the ventricle per beat, while cardiac index reflects blood flow per minute normalized by body surface area.
Can a normal blood pressure occur with a low cardiac index?
Yes. Compensatory vasoconstriction can preserve blood pressure even when flow is reduced.
Can this calculator replace medical assessment?
No. This tool is educational and informational. Clinical decisions should always be made by qualified healthcare professionals.