Calculate cardiac index, cardiac output, or body surface area from measured output or heart rate and stroke volume, with metric and US height and weight units.
Medical disclaimer: For informational/educational purposes only; not medical advice. Do not use this calculator to diagnose, treat, or make urgent medical decisions. Consult a licensed clinician. If you have chest pain, severe shortness of breath, fainting, or other emergency symptoms, seek emergency care.
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Cardiac Index Formula
The cardiac index adjusts cardiac output for body surface area. The base units used are liters per minute for cardiac output, square meters for body surface area, and liters per minute per square meter for cardiac index.
- CI = cardiac index, usually in L/min/m²
- CO = cardiac output, usually in L/min
- BSA = body surface area, usually in m²
Choose a solve mode to use the corresponding rearranged formula:
- To calculate cardiac index: enter cardiac output and body surface area.
- To calculate cardiac output: enter cardiac index and body surface area.
- To calculate body surface area: enter cardiac output and cardiac index.
The calculator also converts supported units before applying the formula. For example, mL/min is divided by 1,000, mL/s is multiplied by 0.06 to obtain L/min, and ft² is multiplied by 0.09290304 to obtain m². When height and weight are used, BSA is estimated with the Mosteller formula: √(height cm × weight kg ÷ 3600). Cardiac output from heart rate and stroke volume is HR × SV ÷ 1000 in L/min.
Common Cardiac Index Reference Ranges
Cardiac index ranges vary by age, clinical condition, measurement method, and treatment context. The values below are broad adult reference points for interpreting a result.
| Cardiac Index | General Interpretation | Notes |
|---|---|---|
| Below 2.5 L/min/m² | Low | May indicate reduced cardiac performance, depending on the clinical setting. |
| 2.5 to 4.0 L/min/m² | Common adult resting range | Often used as a typical reference range, not a diagnosis by itself. |
| Above 4.0 L/min/m² | High | Can occur with increased metabolic demand, sepsis, anemia, exercise, or other conditions. |
Supported Unit Conversions
| Measurement | Supported Units | Base Conversion |
|---|---|---|
| Cardiac output | L/min, mL/min, mL/s | 1 mL/min = 0.001 L/min; 1 mL/s = 0.06 L/min |
| Body surface area | m², ft² | 1 ft² = 0.09290304 m² |
| Cardiac index | L/min/m², mL/min/m², mL/s/m² | 1 mL/min/m² = 0.001 L/min/m²; 1 mL/s/m² = 0.06 L/min/m² |
Example Calculations
Example 1: Calculate cardiac index
You have a cardiac output of 5.6 L/min and a body surface area of 1.8 m².
The cardiac index is 3.11 L/min/m².
Example 2: Calculate cardiac output
You have a cardiac index of 3.0 L/min/m² and a body surface area of 2.0 m².
The cardiac output is 6.0 L/min.
FAQs
What is the difference between cardiac output and cardiac index?
Cardiac output is the total amount of blood the heart pumps per minute. Cardiac index is cardiac output adjusted for body surface area. This makes it easier to compare cardiac performance between people of different body sizes.
What is a normal cardiac index?
A commonly cited adult resting range is about 2.5 to 4.0 L/min/m². Values outside this range should be interpreted with the full clinical picture, including symptoms, blood pressure, heart rate, oxygenation, medications, and how the measurement was obtained.
Why does body surface area affect cardiac index?
Larger bodies generally require more blood flow than smaller bodies. Dividing cardiac output by body surface area normalizes the value, so the result reflects blood flow relative to body size rather than total flow alone.
