How this instrument works
Cardiac output is the volume of blood the heart pumps in one minute, and it comes from just two building blocks: heart rate, how many times the heart beats per minute, and stroke volume, how much blood is ejected with each of those beats. Multiply the two and divide by 1000 to convert millilitres to litres, and the result is a single figure that describes the whole circulation's throughput — the fundamental output of the heart as a pump.
A resting healthy adult typically sits somewhere between about 4 and 8 litres per minute, though the exact figure shifts with body size, fitness, posture, and the demands the body is placing on the circulation at that moment. Two very different hearts can land on the same number: a sedentary heart beating quickly with a modest stroke volume, and a trained athlete's heart beating slowly but ejecting far more with every contraction. Both patterns move similar volumes of blood; they just get there differently.
This figure is the starting point several other cardiovascular calculations build from — cardiac index, a sibling calculator on this site, divides cardiac output by body surface area to judge whether that output is actually adequate for a given person's size. On its own, cardiac output describes total flow. It says nothing about blood pressure, oxygen delivery, or how the heart is coping — those need additional numbers layered on top, which is exactly what StatPearls' physiology overview of cardiac output describes in more clinical depth.
- Enter Heart rate (bpm) — the number of beats per minute, from a pulse count or monitor reading.
- Enter Stroke volume (mL) — the volume ejected by the heart with each single beat.
- Read Cardiac output (L/min) — the calculator multiplies the two and divides by 1000 to convert units.
- Compare the result against the roughly 4-8 L/min range typically cited for a resting adult, keeping in mind that exercise, fever, and other states raise it well above that band.
- Feed the result into the cardiac index calculator alongside a body surface area figure if you want output judged relative to body size.
Worked example — 70 bpm, 70 mL stroke volume
A resting adult with a heart rate of 70 bpm and a stroke volume of 70 mL: 70 × 70 = 4900 mL per minute, and dividing by 1000 gives 4.9 L/min — comfortably inside the roughly 4-8 L/min range typically cited for a healthy resting adult.
Now compare two very different hearts reaching a similar destination. A faster, smaller-volume heart at 100 bpm with a 50 mL stroke volume computes as 100 × 50 ÷ 1000 = 5.0 L/min. A well-conditioned athlete's heart, slower and ejecting much more per beat, at 40 bpm with a 100 mL stroke volume computes as 40 × 100 ÷ 1000 = 4.0 L/min. All three land near the same total cardiac output despite strikingly different heart rates and stroke volumes — a reminder that the two factors trade off against each other.
Questions
What counts as a normal cardiac output?
Roughly 4 to 8 litres per minute for a resting healthy adult, though the figure scales with body size — a larger body generally needs a somewhat higher output to meet its metabolic demand at rest, which is exactly why cardiac index exists to adjust for that.
Why do a slow heart rate and a fast heart rate give the same cardiac output?
Because cardiac output is a product, not either factor alone. A well-trained heart beats slower but ejects more blood per beat, so a low heart rate paired with a large stroke volume can reach the same total output as a faster heart rate paired with a smaller stroke volume — different mechanics, similar throughput.
How is stroke volume actually measured?
Clinically, through imaging methods like echocardiography, which estimates the volume of blood in the ventricle before and after a contraction, or through invasive monitoring in critical care settings. This calculator takes stroke volume as a given input rather than deriving it, so accuracy depends entirely on the quality of that upstream measurement.
Does cardiac output change during exercise?
Yes, substantially — it can rise several times above the resting figure as both heart rate and, to a lesser degree, stroke volume increase to meet the muscles' higher oxygen demand. The 4-8 L/min range cited here describes rest, not exertion, so a higher reading taken during activity is expected rather than concerning.
What is the difference between cardiac output and cardiac index?
Cardiac output is the raw volume pumped per minute; cardiac index divides that figure by body surface area so two people of different sizes can be compared fairly. A cardiac output of 4.9 L/min might be adequate for a smaller person and borderline low for a larger one — cardiac index, this site's sibling calculator, makes that distinction explicit.
Can this calculator diagnose a heart condition?
No. It performs one multiplication and division on numbers you supply — it cannot tell you whether your heart rate or stroke volume were measured correctly, nor account for the dozens of other factors a clinician weighs when assessing cardiac function. Use it to understand the arithmetic, not to self-diagnose.
References
Read this first: This instrument computes a screening figure from population formulas — it is not a diagnosis, and it cannot see the whole picture a clinician can. Use it to inform a conversation, not to replace one.