Cardiac Index Calculator — CO and CI
Enter heart rate, stroke volume, height and weight to calculate cardiac output (CO = HR × SV) and cardiac index (CI = CO / BSA) — the body-size-normalised measure of cardiac pump performance.
bpm
mL/beat
cm
kg
Normal: 2.2–4.0 L/min/m². Below 1.8 L/min/m²: haemodynamic criterion for cardiogenic shock.
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Cardiac output
75 × 70 ÷ 1000 = 5.25 - 2
Body surface area (Mosteller)
√(170 × 70 ÷ 3600) = 1.818BSA = √(height_cm × weight_kg ÷ 3600) - 3
Cardiac index
5.25 ÷ 1.818 = 2.89
How does this calculator work?
CO (L/min) = HR × SV / 1,000. BSA = √(height_cm × weight_kg / 3,600) m² (Mosteller). CI = CO / BSA. Normal CI is 2.2–4.0 L/min/m²; CI below 1.8 indicates cardiogenic shock. At 75 bpm, 70 mL SV, 170 cm, 70 kg: CO ≈ 5.25 L/min, BSA ≈ 1.82 m², CI ≈ 2.89 L/min/m² (normal).
Formula
How this is calculated
Cardiac output (CO) is the volume of blood the heart ejects per minute: heart rate (bpm) multiplied by stroke volume (mL/beat), divided by 1,000 to convert to litres. While CO is a fundamental haemodynamic variable, it does not account for body size — a larger person naturally requires higher CO to perfuse their greater tissue mass. Cardiac index (CI) corrects for this by dividing CO by body surface area (BSA), expressed in m², giving a size-independent value that is comparable across patients.
BSA is estimated here using the Mosteller formula: BSA = √(height_cm × weight_kg / 3,600). Mosteller is one of the simplest and most widely used BSA equations in clinical practice; it agrees closely with the Du Bois formula across typical adult body dimensions. The normal resting cardiac index in healthy adults is 2.2–4.0 L/min/m², with a population mean near 3.1 L/min/m². A CI persistently below 2.2 suggests reduced cardiac reserve; below 1.8 L/min/m² in the presence of hypotension and end-organ signs defines cardiogenic shock by haemodynamic criteria.
In clinical practice, stroke volume is not measured directly without invasive monitoring (pulmonary artery catheter, echocardiography, pulse-contour analysis). This calculator accepts SV as a user input, appropriate for values derived from bedside echocardiography or continuous cardiac output monitors. The population distribution shown is illustrative (mean 3.1, SD 0.6 L/min/m²) based on published reference data from resting healthy adults; individual normal ranges vary with age, fitness level and clinical context.
Frequently asked questions
Normal resting CI in adults is 2.2–4.0 L/min/m². Values consistently below 2.2 suggest low cardiac output and possible heart failure; below 1.8 L/min/m² with clinical signs of hypoperfusion (hypotension, oliguria, altered consciousness) meets the haemodynamic definition of cardiogenic shock. Highly trained athletes may have CI above 4.0 at rest due to high stroke volumes.
Stroke volume is measured or derived by echocardiography (Doppler LVOT velocity-time integral × LVOT cross-sectional area), pulse-contour analysis systems (PiCCO, LiDCO, ClearSight) or thermodilution via a pulmonary artery catheter. In the absence of direct measurement, normal resting SV is typically 60–100 mL/beat for a healthy adult. Critically ill patients often have SV 30–60 mL/beat.
Cardiac workload scales with metabolic rate, which correlates better with body surface area than weight alone — this is known as the "surface law" in physiology. BSA normalisation yields CI values that are broadly comparable across patients of different sizes, ages and sexes. Weight-based normalisation (cardiac output per kg) is used in paediatric and neonatal cardiology, where BSA is small and formulae differ.
TG we-Calculate Editorial Team. (2026). Cardiac Index Calculator — CO and CI [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/cardiac-index-calculator
TG we-Calculate Editorial Team. "Cardiac Index Calculator — CO and CI." TG we-Calculate. 2026. https://we-calculate.com/calculator/cardiac-index-calculator.
TG we-Calculate Editorial Team, "Cardiac Index Calculator — CO and CI," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/cardiac-index-calculator
@misc{wecalculate_cardiac_index_calculator, title = {Cardiac Index Calculator — CO and CI}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/cardiac-index-calculator}}, year = {2026}, note = {TG we-Calculate} }
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