Cardiac Output Calculator
Cardiac output is the volume of blood your heart pumps each minute. Use heart rate times stroke volume, the oxygen based Fick method, or reverse solve for heart rate or stroke volume. Add height and weight to also see cardiac index, stroke volume index, and ejection fraction.
Formula
Worked example
With a heart rate of 70 bpm and stroke volume of 70 mL: CO = 70 × 70 ÷ 1000 = 4.9 L/min. For a 175 cm, 75 kg adult the Mosteller BSA is √(175 × 75 ÷ 3600) ≈ 1.91 m², so cardiac index = 4.9 ÷ 1.91 ≈ 2.57 L/min/m². By the Fick method, VO2 of 250 mL/min with Hb 15 g/dL, SaO2 98% and SvO2 70% gives an A-V difference of 1.34 × 15 × 0.28 ≈ 5.63 mL/dL, so CO = 250 ÷ 56.3 ≈ 4.44 L/min.
What cardiac output measures
Cardiac output is the total volume of blood the heart pumps into the circulation each minute, the product of heart rate (beats per minute) and stroke volume (the millilitres ejected with each beat). Because stroke volume is in millilitres, the raw product is in mL/min, so the calculator divides by 1,000 to give litres per minute. A healthy adult at rest typically has a cardiac output of about 4 to 8 L/min, enough to deliver oxygen and nutrients to every tissue and carry away waste. This tool lets you compute it three ways: the simple heart rate times stroke volume product, the oxygen based Fick method used in catheter labs, and a reverse solve that finds the heart rate or stroke volume needed to hit a target output.
The Fick method
The Fick principle states that the oxygen your tissues consume equals blood flow multiplied by the amount of oxygen each litre of blood gives up. Rearranged, cardiac output equals oxygen consumption (VO2) divided by the arterial to venous oxygen content difference. The content difference is found from hemoglobin and the gap between arterial (SaO2) and mixed venous (SvO2) saturations, using 1.34 mL of oxygen carried per gram of hemoglobin. A resting adult consumes roughly 250 mL of oxygen per minute, or about 125 mL/min per square metre of body surface area. The Fick method is considered the clinical reference standard because it measures flow directly from oxygen balance rather than estimating stroke volume.
Cardiac index, stroke volume index and body size
A 4.5 L/min output means something different for a small person than a large one, so clinicians divide cardiac output by body surface area (BSA) to get the cardiac index in litres per minute per square metre, normally 2.5 to 4.0. Dividing stroke volume by BSA gives the stroke volume index, normally about 33 to 47 mL/m². This calculator estimates BSA from your height and weight with the Mosteller formula, the square root of height in centimetres times weight in kilograms divided by 3,600, or you can enter a measured BSA. Indexing lets the same thresholds apply across people of very different builds, which is why intensive care and cardiology teams track index values rather than raw output.
Ejection fraction and how the numbers change
Turn on ejection fraction to enter the left ventricle end diastolic volume (EDV, when full) and end systolic volume (ESV, after it contracts). Stroke volume is EDV minus ESV, and ejection fraction is that stroke volume as a percentage of EDV, normally 55 to 70%. At rest the heart turns over only a fraction of its capacity; during hard exercise both heart rate and stroke volume rise and cardiac output can reach 20 to 25 L/min in untrained adults and 35 to 40 L/min in elite athletes. Heart failure, blood loss, severe dehydration or arrhythmias can drop output below what tissues need. These values are estimates for education and self tracking, not a diagnosis, and any concern about your heart should be reviewed by a qualified medical professional.
Typical adult resting values
| Measure | Typical range | Status |
|---|---|---|
| Heart rate | 60-100 bpm | Normal |
| Stroke volume | 60-100 mL | Normal |
| Cardiac output | 4-8 L/min | Normal |
| Cardiac index | 2.5-4.0 L/min/m² | Normal |
| Stroke volume index | 33-47 mL/m² | Normal |
| Ejection fraction | 55-70% | Normal |
Reference ranges for a healthy adult at rest. Individual values vary with size, fitness and clinical condition.
Frequently asked questions
What is a normal cardiac output?
For a resting adult, a cardiac output of roughly 4 to 8 litres per minute is normal. The cardiac index, which adjusts for body size, normally sits between 2.5 and 4.0 L/min/m². Values outside these bands can be normal during exercise or may warrant medical assessment at rest.
How does the Fick method calculate cardiac output?
The Fick method divides oxygen consumption (VO2) by how much oxygen each litre of blood delivers, found from hemoglobin and the difference between arterial and mixed venous oxygen saturations. The formula is CO = VO2 ÷ (1.34 × hemoglobin × (SaO2 - SvO2) × 10). It is the clinical reference standard because it measures flow directly from oxygen balance.
Can I work backwards to find heart rate or stroke volume?
Yes. Choose a reverse solve mode and enter a target cardiac output plus either the stroke volume or the heart rate. Because CO = HR × SV, the calculator rearranges the equation to find the missing value, which is useful for understanding how fast or how strongly the heart must work to meet a given demand.
How do I find my stroke volume or ejection fraction?
Stroke volume and ejection fraction are usually measured with echocardiography or invasive monitoring, not at home. A typical resting stroke volume is 60 to 100 mL and a normal ejection fraction is 55 to 70%. If you have measured end diastolic and end systolic volumes, enter them and the calculator finds stroke volume (EDV minus ESV) and ejection fraction for you.