Cardiac Output Calculator

Your cardiac output is how much blood your heart pumps each minute. For most adults at rest that lands around five liters, close to your entire blood volume recirculating once a minute. The math is straightforward: multiply heart rate by stroke volume. Plug in both numbers below and you get cardiac output in L/min, with unit switches if you need them.

What is cardiac output?

Cardiac output (CO) is the volume of blood your heart pumps in one minute. It comes from two things: how fast the heart beats, and how much blood it pushes out per beat. A healthy adult at rest sits near 5 L/min, which is roughly a complete turnover of your blood every minute. Start running and both numbers climb fast. Your heart rate might jump from 70 to 150, and stroke volume from 70 mL to 100 mL per beat, pushing cardiac output past 15 L/min so your working muscles get the oxygen they need.

How to use this calculator

Put your heart rate in beats per minute. If you don't have a monitor, count your pulse for fifteen seconds and multiply by four. Then enter stroke volume in milliliters. This one is harder to know without imaging like an echocardiogram, but adult resting stroke volume usually falls between 60 and 100 mL. The result is cardiac output in liters per minute. The unit dropdowns let you switch to other units when it's convenient.

The formula, with a worked example

CO = HR \times SV

Say you're 30, resting, with a heart rate of 72 bpm and a stroke volume of 70 mL per beat:

CO = 72 \, \text{bpm} \times 70 \, \text{mL/beat} = 5{,}040 \, \text{mL/min}

Or about $5.04 \, \text{L/min}$ . Now imagine you start running. Heart rate climbs to 160, stroke volume to 110:

CO = 160 \times 110 = 17{,}600 \, \text{mL/min} = 17.6 \, \text{L/min}

More than triple the resting value, which is roughly what you'd expect for serious exertion in a fit person.

Normal ranges and what they mean

At rest, most healthy adults fall between 4 and 8 L/min, with bigger bodies on the higher end. Moderate exercise pushes that to 10 to 15 L/min. Elite endurance athletes can reach 30 to 40 L/min at peak effort, mostly because years of training have remodeled the heart to push more blood per beat. A resting CO under 4 L/min can be a sign of heart failure or severe deconditioning. Resting values above 8 L/min sometimes show up with hyperthyroidism or anemia, where metabolic demand is unusually high.

What controls cardiac output

Four levers do most of the work. Preload is how much the heart muscle stretches before it contracts; a fuller stretch generally produces a stronger contraction and a bigger stroke volume. Contractility is how forcefully the muscle squeezes once it's loaded, and adrenaline raises it. Afterload is the pressure the heart has to push against to eject blood, so chronically high blood pressure eats into stroke volume. The autonomic nervous system tunes heart rate and contractility from second to second. A scare, a hard sprint, or a stressful meeting all flip the sympathetic switch and push both numbers up at once.

Frequently asked questions

How accurate is this calculator?

The arithmetic is exact; it's just multiplication. The result is only as good as the numbers you put in. Heart rate is easy to measure precisely. Stroke volume usually needs echocardiography or cardiac MRI to pin down. If you're plugging in a typical value rather than a measured one, treat the answer as a ballpark.

Why does cardiac output rise during exercise?

Working muscles need a lot more oxygen, and the heart delivers it by beating faster and pushing more blood out per beat at the same time. The sympathetic nervous system runs that response, mostly through adrenaline.

What if I only know my heart rate?

You can estimate. Adult resting stroke volume averages around 70 to 80 mL for men and 60 to 70 mL for women. Trained endurance athletes often sit higher, around 90 to 110 mL, because training has enlarged the heart's chambers. Take the estimate with a grain of salt; individual variation is wide.

Can I use this for clinical diagnosis?

No. This is here to help you learn the math. Actual clinical assessment of cardiac output needs proper equipment and a clinician to interpret it. Don't use this tool to diagnose or guide treatment without talking to a doctor.

Why do trained athletes have such low resting heart rates?

Endurance training enlarges the heart's chambers, so each beat pumps more blood. Since resting cardiac output still needs to land near 5 L/min, a larger stroke volume means fewer beats per minute will get there. Someone with a 100 mL stroke volume only needs about 50 bpm at rest. A person with a 70 mL stroke volume needs about 71 bpm to hit the same total.