Cardiac Output Calculator

Formula Used by the Calculator

The calculator uses the standard cardiac output formula:

Cardiac output (L/min) = Heart rate (beats/min) × Stroke volume (mL) ÷ 1000

Written more compactly:

Where:

• CO is cardiac output in liters per minute (L/min).
• HR is heart rate in beats per minute (bpm).
• SV is stroke volume in milliliters (mL) per beat.

The division by 1000 simply converts the product of HR and SV from milliliters per minute into liters per minute (1000 mL = 1 L).

How to Enter Your Heart Rate and Stroke Volume

Heart rate (beats per minute)

Your heart rate is usually the easier value to measure yourself. You can obtain it by:

• Using a fitness tracker, smartwatch, or chest‑strap heart rate monitor.
• Using a home blood pressure monitor that shows pulse rate.
• Measuring manually at the wrist or neck for 30–60 seconds and converting to beats per minute.

For resting measurements, sit quietly for several minutes beforehand, then measure. Resting adult heart rate commonly falls between about 60 and 100 bpm, but trained athletes may have resting values as low as 40–50 bpm.

Stroke volume (mL per beat)

Stroke volume is harder to measure outside of a clinical or research setting. Doctors typically estimate it using:

• Echocardiography (heart ultrasound).
• Cardiac MRI or other imaging‑based methods.
• Specialized catheter‑based techniques in intensive care units.

If you do not have a measured stroke volume, you can use a reasonable estimate for resting conditions. Many healthy adults at rest have stroke volumes around 60–100 mL per beat. Larger, fitter individuals and endurance‑trained athletes may have higher stroke volumes even at rest.

Practical tip: If you are unsure, you might start with 70 mL as a mid‑range resting estimate, then see how the result compares with the typical ranges described below.

Typical Cardiac Output Values

Cardiac output varies with age, body size, fitness level, and whether you are resting or exercising. The examples below refer to typical adults without known severe heart disease.

In many adults, resting cardiac output typically falls in the range of about 4–8 L/min. During moderate to intense exercise, it can increase several‑fold to meet the body’s increased oxygen demand.

Worked Examples

Example 1: Typical resting adult

Suppose you measure your resting heart rate as 72 bpm and use an estimated stroke volume of 70 mL.

1. Multiply heart rate by stroke volume: 72 × 70 = 5040 mL per minute.
2. Convert to liters per minute by dividing by 1000: 5040 ÷ 1000 = 5.04 L/min.

Your estimated cardiac output would be about 5.0 L/min, which sits comfortably within the usual resting range for adults.

Example 2: Exercise value

Now imagine you are doing brisk cycling. Your fitness tracker shows a heart rate of 130 bpm. You assume your stroke volume has increased to around 100 mL per beat.

1. Multiply heart rate by stroke volume: 130 × 100 = 13,000 mL per minute.
2. Convert to liters: 13,000 ÷ 1000 = 13 L/min.

Your estimated cardiac output is 13 L/min, showing how much more work your heart is doing to supply your muscles during exercise.

How to Interpret Your Result

The calculator output is an estimate in liters per minute. Interpreting it always depends on the clinical context, your body size, and whether you are resting or active. The following broad guidance applies to many adults but does not replace personalized medical advice.

• Lower than about 4 L/min at rest: In some people, a lower value could be normal (for example, a small, relaxed individual or an athlete with a slow heart rate). In others, especially if accompanied by shortness of breath, dizziness, or fatigue, it could reflect reduced cardiac output and should prompt discussion with a healthcare professional.
• Roughly 4–8 L/min at rest: This is a commonly cited resting range for many adults. Values here are often considered typical, although “normal” depends strongly on individual factors.
• Above about 8 L/min at rest: A higher resting cardiac output can occur in larger individuals, during fever, pregnancy, anemia, hyperthyroidism, or other high‑flow states. Persistent high values at rest, particularly with symptoms, should be evaluated by a clinician.

During exercise, it is expected for cardiac output to rise significantly. Healthy younger adults may reach 15–20 L/min or more at maximal effort, while highly trained endurance athletes may exceed this.

Important: Because stroke volume is often estimated, your true cardiac output may differ from the calculated value. Any concerning symptoms (chest pain, breathlessness, fainting, swelling of the legs, or unexplained fatigue) warrant prompt medical assessment, regardless of what this calculator shows.

Factors That Affect Cardiac Output

Several physiological and medical factors influence both stroke volume and heart rate, and therefore cardiac output:

• Blood volume and hydration: Dehydration tends to reduce the amount of blood returning to the heart, which can decrease stroke volume. Fluid overload or certain kidney and heart conditions can increase volume and sometimes raise cardiac output.
• Blood pressure and vascular resistance: High blood pressure increases the resistance against which the heart must pump. Over time, this can strain the heart and alter stroke volume.
• Heart muscle function: Conditions such as heart failure, cardiomyopathy, or prior heart attacks can impair the heart’s ability to contract effectively, lowering stroke volume and cardiac output.
• Heart rhythm: Arrhythmias (irregular heartbeats) can reduce the efficiency of filling and ejection, sometimes significantly affecting cardiac output.
• Autonomic nervous system and hormones: Stress, anxiety, thyroid hormones, and medications (such as beta‑blockers or stimulants) can raise or lower heart rate and contractility.
• Physical conditioning: Regular aerobic exercise usually increases stroke volume and can lower resting heart rate, leading to an efficient heart that maintains adequate cardiac output with fewer beats.

Comparison With Related Heart Measures

Cardiac output is closely related to several other cardiovascular measurements. The table below summarizes key differences.

Assumptions and Limitations

This calculator uses a simplified equation and user‑provided inputs. It does not capture all the nuances of cardiovascular physiology. Key assumptions and limitations include:

• Estimated stroke volume: Unless measured with medical imaging or specialized devices, stroke volume values are approximate. Small changes in the value you enter can noticeably alter the cardiac output result.
• Stable rhythm: The formula assumes a relatively steady heart rhythm. In people with irregular rhythms (such as atrial fibrillation), beat‑to‑beat variation can make simple calculations less reliable.
• Single time point: The calculation reflects one moment in time. Cardiac output can fluctuate with posture, breathing, emotions, temperature, medications, and recent activity.
• No indexing to body size: The tool reports total cardiac output, not cardiac index (cardiac output adjusted for body surface area). Two people with the same output but very different body sizes may not have the same cardiovascular status.
• Educational use only: Results are not intended for emergency assessment, medication dosing, or any critical medical decision‑making.

Medical Disclaimer and When to Seek Care

This cardiac output calculator is for general educational purposes only and is not a substitute for professional medical evaluation, diagnosis, or treatment.

Always consult a qualified healthcare professional if you:

• Have chest pain, pressure, or discomfort.
• Experience shortness of breath at rest or with minimal exertion.
• Notice rapid, irregular, or very slow heartbeats.
• Have episodes of dizziness, fainting, or near‑fainting.
• See swelling of the legs, ankles, or abdomen.

In a medical emergency, call your local emergency number immediately.

Sources and Further Reading

For readers who want to explore cardiac output and related topics in more depth, the following sources provide detailed, peer‑reviewed information:

• Guyton and Hall. Textbook of Medical Physiology. Elsevier.
• Braunwald’s Heart Disease: A Textbook of Cardiovascular Medicine. Elsevier.
• American Heart Association – resources on heart failure, cardiac function, and exercise.

Related Calculators

You may also find these tools helpful for understanding your cardiovascular health (availability may vary on this site):

• Stroke Volume Estimator
• Mean Arterial Pressure (MAP) Calculator
• Heart Rate Zone Calculator for Exercise