Formula and Method for the Cardiac Output Calculator
Cardiac output (CO) is the volume of blood the heart pumps in one minute, and it is the product of how fast the heart beats and how much blood it ejects with each beat: CO (L/min) = HR (beats/min) × SV (mL/beat) ÷ 1000. This calculator also converts your result into cardiac index (CI), which adjusts cardiac output for body size using body surface area (BSA), so it can be compared fairly across different-sized people. This tool is educational — it does not replace a clinical measurement (such as echocardiography or thermodilution) or a physician's assessment.
How the calculation works
Enter heart rate (HR) and stroke volume (SV, the amount of blood ejected per heartbeat) to get cardiac output: CO = HR × SV ÷ 1000, where dividing by 1000 converts milliliters to liters. Enter height and weight (in either metric or imperial units) to estimate body surface area using the Mosteller formula, BSA (m²) = √(height (cm) × weight (kg) ÷ 3600). Cardiac index is then CO ÷ BSA, expressed in L/min/m². The calculator compares both CO and CI against typical resting-adult reference ranges — roughly 4.0–8.0 L/min for cardiac output and 2.5–4.0 L/min/m² for cardiac index.
Common mistakes
- Forgetting to convert units: stroke volume is measured in milliliters, but cardiac output is reported in liters per minute — skipping the ÷1000 step overstates CO by a factor of 1000.
- Confusing cardiac output with cardiac index: a large athlete and a small adult can have the same CO but very different CI once body size is taken into account.
- Using a non-resting heart rate: HR measured right after exercise, caffeine, or stress will inflate CO relative to standard resting reference ranges.
Real-world applications
- Anesthesiology and critical-care monitoring use cardiac output and cardiac index to track how well the heart is meeting the body's circulatory demands.
- Exercise physiology uses cardiac output to explain how the heart adapts to activity — increasing mainly through stroke volume in trained athletes and through heart rate in untrained individuals.
- Heart failure management uses trends in cardiac index, alongside other clinical measurements, to help gauge how effectively the heart is pumping over time.
This calculator is for general education and self-tracking only. It is not a diagnostic tool, and it should never be used to make medication, treatment, or emergency-care decisions. If you have symptoms such as chest pain, shortness of breath, or fainting, seek medical care immediately, and discuss any calculated values with a qualified healthcare provider.