Cardiac output from heart rate and stroke volume, with optional cardiac index context Use this cardiac output calculator to turn a heart rate and stroke volume pair into litres per minute, then compare the result with cardiac index and simple sensitivity rows instead of reading one isolated number.
Quick scenarios
Optional: cardiac index (height and weight)
Cardiac output sheet
4.9 L/min
Normal resting cardiac output range. This page uses the simple heart rate × stroke volume model, then optionally normalises the result to body surface area with the Mosteller formula and turns the same estimate into comparison rows.
70
Heart rate (bpm)
70
Stroke volume (mL)
4900
mL / min
294
L / hour
81.67
mL / sec
Calculation sheet
Working formula
70 bpm × 70 mL ÷ 1000 = 4.9 L/min
Cardiac output interpretation
Normal resting cardiac output range
What changes the estimate fastest
These comparison rows keep the same basic scenario and show how a 10 bpm or 10 mL shift would move the output. They are educational comparisons, not a substitute for measured haemodynamics.
Scenario
HR
SV
CO
Current inputs
70 bpm
70 mL
4.9 L/min
Heart rate +10 bpm
80 bpm
70 mL
5.6 L/min
Heart rate -10 bpm
60 bpm
70 mL
4.2 L/min
Stroke volume +10 mL
70 bpm
80 mL
5.6 L/min
Stroke volume -10 mL
70 bpm
60 mL
4.2 L/min
Reference ranges
Resting values are usually interpreted alongside symptoms, blood pressure, rhythm, and
the clinical setting.
Metric
Reference range
Interpretation
Cardiac output
4.0–8.0 L/min
Common adult resting reference range.
Cardiac index
2.5–4.0 L/min/m²
Common adult resting reference range when body size is taken into account.
Clinical caution These are reference estimates only. Cardiac output can vary with fever, anaemia, fitness level, pregnancy, medications, hydration status, and acute illness. A normal-looking number does not rule out symptoms or disease, and a low or high value must be interpreted in clinical context.
People searching for a cardiac output calculator usually want three things: the core heart rate × stroke volume formula, a sense of whether the answer sits in a normal resting range, and a quick way to compare cardiac output with cardiac index.
The cardiac output formula
Cardiac output (CO) equals heart rate multiplied by stroke volume. A normal resting cardiac output in adults is typically 4–8 L/min, though values outside this range may still be physiologic depending on body size, fitness level, fever, anaemia, or haemodynamic state.
Some clinical calculators estimate cardiac output using the Fick principle or Doppler echocardiography. This page uses the simpler HR × SV model because that is the expression many searchers are looking for when they type cardiac output formula or how to calculate cardiac output.
CO (L/min) = HR (bpm) × SV (mL) ÷ 1000
Heart rate × stroke volume gives cardiac output. Divide mL by 1000 to convert to litres per minute.
Cardiac index
Because cardiac output varies with body size, the cardiac index (CI) normalises it to body surface area: CI = CO ÷ BSA. Body surface area uses the Mosteller formula: BSA = √(height × weight ÷ 3600). A normal resting cardiac index is typically 2.5–4.0 L/min/m².
That is why cardiac output and cardiac index often appear together in search results. One gives you the raw flow in litres per minute, while the other makes that number easier to compare between people of different sizes.
How cardiac output is measured in practice
In clinical care, cardiac output may be estimated from echocardiography, thermodilution, impedance methods, or the Fick principle. The Fick approach uses oxygen consumption and the arterial-venous oxygen difference, which is why some specialised calculators focus on cardiac index or Fick output rather than the HR × SV equation used here.
That distinction matters for search intent as well. People looking for a cardiac output calculator, cardiac index calculator, Fick cardiac output calculator, or normal cardiac output usually want related but slightly different answers, so a good page should explain which method it is using and why.
Clinical interpretation
Low cardiac output may suggest heart failure, hypovolaemia, or severe bradycardia. Elevated output at rest can occur with fever, anaemia, thyrotoxicosis, or high physical fitness. During vigorous exercise, cardiac output can increase 4–5 times above resting values in trained athletes. Stroke volume is not routinely measured in clinical practice and is usually derived from echocardiography, thermodilution, or non-invasive cardiac monitoring.
Worked example: 70 bpm and 70 mL
If heart rate is 70 beats per minute and stroke volume is 70 mL per beat, cardiac output is 4.9 L/min because 70 × 70 = 4900 mL/min, or 4.9 litres per minute. That sits inside the common adult resting reference range of 4–8 L/min.
If the same person is 170 cm tall and weighs 70 kg, Mosteller body surface area is about 1.82 m². Cardiac index is then about 2.69 L/min/m², which also sits inside the common resting reference range of 2.5–4.0 L/min/m².
Why heart rate and stroke volume do not change the result in the same clinical way
Mathematically, cardiac output changes whenever either heart rate or stroke volume changes. Clinically, though, a 10 bpm increase and a 10 mL increase are not interchangeable explanations. A faster rate may reflect fever, stress, arrhythmia, pain, or compensation for low stroke volume, while a larger stroke volume may reflect training adaptation, preload, or better contractile performance.
That is why the updated calculator now shows sensitivity rows instead of only the final answer. The rows help explain what happens if heart rate changes while stroke volume stays fixed, or if stroke volume changes while heart rate stays fixed. This does not diagnose the reason for the change, but it makes the mechanics of the formula much easier to understand.
Why cardiac index can be more informative than cardiac output alone
Raw cardiac output is useful, but it can be misleading when comparing people of different body sizes. A flow of 5.0 L/min may be completely ordinary for one adult and less reassuring for another if body surface area is very different. That is exactly why cardiac index exists: it normalises flow to body size.
The updated page therefore keeps the body-size checkpoints visible when height and weight are entered. Those rows show how common resting cardiac-output values would translate into cardiac index for the same body surface area. It is a practical way to understand why one normal cardiac output range does not fit every adult equally well.
Why a normal-looking number does not rule out symptoms
A calculator can only work with the numbers entered. It cannot see blood pressure, oxygen extraction, rhythm irregularity, valve disease, ventricular function, or whether the measurement conditions were stable. That means a cardiac output inside the common resting range is not the same thing as a normal cardiovascular assessment.
This matters especially for people searching phrases like normal cardiac output or normal cardiac index. Those ranges are useful educational anchors, but they are not stand-alone rules for ruling in or ruling out disease. Symptoms, examination findings, imaging, and the method used to obtain stroke volume still matter more than the calculator output by itself.
What happens to cardiac output during exercise or high-output states
Resting reference ranges should not be applied blindly to exercise, fever, anaemia, sepsis, pregnancy, or high training status. During exercise, both heart rate and stroke volume can rise substantially, which is why cardiac output may increase several-fold above resting values without being pathological. In high-output states, the number can also rise because metabolic demand is higher or because the circulation is compensating for another problem.
That is why the page frames the result specifically as a resting reference worksheet unless you intentionally use it to understand a known scenario. The formula still works in exercise or high-output settings, but the interpretation changes, and the resting reference table stops being the right anchor.
Frequently asked questions
What is a normal cardiac output at rest?
For most adults, a resting cardiac output of 4–8 L/min is considered normal. Trained endurance athletes often have higher stroke volumes and lower resting heart rates, keeping cardiac output in a similar range.
What is the difference between cardiac output and cardiac index?
Cardiac output measures total blood pumped per minute. Cardiac index normalises this to body surface area, making it more comparable between people of different sizes. A CI of 2.5–4.0 L/min/m² is generally considered normal at rest.
How is stroke volume measured?
Clinically, stroke volume is most commonly estimated from echocardiography or invasive monitoring. It is not typically measured directly in routine care and cannot be calculated without specialised equipment.
What is the Fick equation for cardiac output?
The Fick principle estimates cardiac output from oxygen consumption and the difference between arterial and venous oxygen content. It is useful in catheterisation and advanced hemodynamic assessment, but this page uses the simpler heart rate × stroke volume model.
How does cardiac output change during exercise?
Cardiac output normally rises during exercise because both heart rate and stroke volume increase. The exact rise depends on fitness, workload, hydration, and whether the measurement is taken at rest, during steady exercise, or at peak effort.
What is a normal cardiac index?
A common adult resting reference range is about 2.5 to 4.0 L/min/m², but different references can vary slightly. Cardiac index is often more useful than raw cardiac output when body-size differences matter, because it adjusts flow to body surface area instead of treating all adults as if the same total flow should apply equally.
Can cardiac output be normal if I still have symptoms?
Yes. A normal-looking cardiac output does not rule out symptoms, cardiovascular disease, or haemodynamic problems. Symptoms still need clinical interpretation alongside rhythm, blood pressure, imaging, oxygen delivery, and the method used to estimate stroke volume.
Why does an athlete sometimes have a low heart rate but normal cardiac output?
Because stroke volume can be higher. Endurance-trained athletes often pump more blood with each beat, so a lower resting heart rate can still produce a normal resting cardiac output. That is one reason the formula should be read as a balance between heart rate and stroke volume rather than by heart rate alone.
Can I estimate stroke volume from this page if I only know heart rate?
No. This page needs a stroke-volume value to estimate cardiac output. Stroke volume usually comes from echocardiography, haemodynamic monitoring, or another clinical measurement method. The calculator does not derive it from heart rate alone.
Why is cardiac index sometimes preferred over cardiac output?
Cardiac index is often preferred when comparing people of different body sizes because it divides cardiac output by body surface area. That makes it easier to see whether the flow is adequate relative to the person’s size instead of just looking at total litres per minute.
