Cardiac Index and Stroke Volume Calculator

Index a cardiac output to body surface area and split it into its two factors — rate and stroke volume. The same 5 L/min is generous in one body and inadequate in another.

Last updated 8 Oct 2026

Cardiac index, stroke volume and stroke volume index

CO ÷ BSA, CO ÷ HR

Cardiac output (L/min)From thermodilution, from an uncalibrated pulse-contour monitor, from echocardiography or from the Fick calculation. Indexing does not improve a cardiac output, so the index inherits whatever error the output carried.

Heart rate (per minute)The rate at the time the output was measured. In atrial fibrillation the beat-to-beat stroke volume varies widely and this average stroke volume describes no individual beat.

Height (cm)Body surface area here is the Mosteller formula, the default on this site’s body surface area calculator, where the Du Bois alternative is also available.

Weight (kg)Actual body weight. Indexing to a surface area computed from actual weight is the published convention, and it is also why the index behaves oddly at the extremes of obesity — surface area keeps rising while metabolically active mass does not.

2.59L/min/m²Example

Cardiac output 5.0 L/min, heart rate 78, height 172 cm, weight 78 kg

Three figures from one output

Cardiac index = cardiac output (L/min) ÷ BSA (m²)
Stroke volume = cardiac output (L/min) × 1000 ÷ heart rate
Stroke volume index = stroke volume ÷ BSA
BSA (Mosteller) = √(height cm × weight kg ÷ 3600)

cardiac index: L/min/m². The figure to quote whenever body size is away from average, because every published range for cardiac output was derived in bodies of about 1.7 to 2.0 m²
stroke volume: mL per beat. The × 1000 converts litres to millilitres. Cardiac output has exactly two factors, and knowing which one is doing the work changes the question entirely
stroke volume index: mL/m²/beat. Published range 33 to 47 on both reference cards. It is stroke volume divided by surface area, which is the same as cardiac index divided by heart rate
why indexing is not optional: a 1.4 m² adult and a 2.2 m² adult differ in surface area by more than half. The same 5 L/min is 3.6 L/min/m² in the first and 2.3 in the second — one inside the quoted range and one below it, from the identical measurement
Mosteller or Du Bois: this page uses Mosteller, as the site’s own BSA calculator does by default. Du Bois typically agrees to within 1 to 2%, which is smaller than the error in the cardiac output being indexed
what it does not fix: indexing corrects for size, not for demand. It does not tell you whether the output is enough, and in severe obesity the denominator itself becomes the problem

Worked example

Cardiac output 5.0 L/min, heart rate 78, height 172 cm, weight 78 kg
BSA = √(172 × 78 ÷ 3600) = √3.7267 = 1.93 m²
Cardiac index = 5.0 ÷ 1.9305 = 2.59 L/min/m² — inside the quoted 2.5 to 4.0
Stroke volume = 5.0 × 1000 ÷ 78 = 64.1 mL/beat
Stroke volume index = 64.1 ÷ 1.9305 = 33.2 mL/m²/beat — at the very bottom of the quoted 33 to 47
Now put the identical 5.0 L/min into a 152 cm, 48 kg adult: BSA 1.42 m², index 3.51 L/min/m², above the quoted range
And into a 188 cm, 110 kg adult: BSA 2.40 m², index 2.09 L/min/m², below it. One measurement, three different readings, and the only thing that changed was the body
Hold the output at 5.0 and raise the rate to 130: the stroke volume falls to 38.5 mL/beat while the index does not move at all. The index is blind to how the output is being produced

Published ranges for the three figures

Both cards print cardiac output as HR × SV ÷ 1000 and stroke volume index as CI ÷ HR × 1000, which are the same relations as above rearranged. These four ranges are mutually consistent at a surface area near 1.8 m² and only there — 60 to 100 mL/beat at 33 to 47 mL/m²/beat implies a body of about 1.8 to 2.1 m².
Figure	Range	Units	Source
Cardiac output	4 to 8	L/min	Edwards reference card; identical on the WVU SICU card
Cardiac index	2.5 to 4.0	L/min/m²	Both cards
Stroke volume	60 to 100	mL/beat	Both cards
Stroke volume index	33 to 47	mL/m²/beat	Both cards

The same 5 L/min, indexed into four bodies

Every index in this table is this calculator’s own arithmetic on one unchanged cardiac output. The spread is 1.7-fold, which is larger than most of the clinical differences a cardiac output is quoted to distinguish.
Height and weight	BSA (m²)	Cardiac index	Reads as
152 cm, 48 kg	1.42	3.51	Above the quoted range
165 cm, 60 kg	1.66	3.02	Within the quoted range
172 cm, 78 kg	1.93	2.59	Within the quoted range
188 cm, 110 kg	2.40	2.09	Below the quoted range

One output, two factors, and why the raw number misleads

A cardiac output on its own answers a smaller question than it appears to. Five litres a minute is above the quoted lower bound for an adult, and it is also 3.51 L/min/m² in a small adult and 2.09 L/min/m² in a large one — one comfortably inside the published range and one below it, from the identical measurement. Every reference range for cardiac output was derived in bodies of roughly average size, so the first thing to do with an output measured in a body that is not average is to index it, conventionally to body surface area.

The second thing is to factor it. Cardiac output is heart rate times stroke volume and nothing else, and the two have entirely different implications. An output of 5 L/min at 60 beats per minute is an 83 mL stroke volume and a circulation with room to move; the same 5 L/min at 140 is a 36 mL stroke volume and a patient holding their output together with the one variable they have already used up. Rate also has a cost: shortening diastole shortens coronary filling and leaves less time for the ventricle to fill at all. The index is blind to all of this — it does not move when the rate changes at constant output, which is why both figures belong on one page.

Stroke volume index, stroke volume divided by surface area, is the figure that survives both corrections, and the reference cards put it at 33 to 47 mL/m²/beat. It is worth a glance at how the published ranges fit together: 60 to 100 mL/beat and 33 to 47 mL/m²/beat are only mutually consistent in a body of about 1.8 to 2.1 m². The ranges came from a cohort, not from first principles, and they carry that cohort’s build.

Indexing has a limit, at the top of the weight range. Body surface area keeps rising with weight while metabolically active tissue does not, so dividing by surface area systematically understates the cardiac index of a very obese patient — the denominator, not the circulation, is what changed. There is no agreed correction, and the honest response is to say which surface area formula was used and to follow the trend in one patient rather than the absolute value against a population. Every figure here is derived from other measurements, so it carries their errors as well as its own. A derived index is never more reliable than the least reliable number that went into it. A derived haemodynamic number is read alongside the patient — the history, the perfusion, the lactate, the trend across serial measurements — and never instead of them. It supports a clinician’s judgement rather than replacing it.

Frequently asked questions

What is a normal cardiac index?

2.5 to 4.0 L/min/m² at rest, on both the Edwards Lifesciences and West Virginia University SICU reference cards. The corresponding cardiac output range on the same cards is 4 to 8 L/min, which only agrees with the index range in a body of roughly 1.6 to 2.0 m². Both are population figures from reference cards rather than limits, and your own unit’s values take precedence.

How do I calculate stroke volume from cardiac output?

Divide the cardiac output in litres per minute by the heart rate and multiply by 1000. At 5.0 L/min and 78 beats per minute that is 64.1 mL/beat. The published range is 60 to 100 mL/beat, and 33 to 47 mL/m²/beat once indexed to body surface area.

Why index cardiac output to body surface area at all?

Because the same output means different things in different bodies. Put an unchanged 5.0 L/min into a 152 cm, 48 kg adult and the index is 3.51 L/min/m², above the quoted range; put it into a 188 cm, 110 kg adult and it is 2.09, below it. That 1.7-fold spread is bigger than most of the differences a cardiac output is measured to detect.

Does a normal cardiac index mean perfusion is adequate?

No, and this page does not say so. Indexing corrects for body size, not for demand, and demand is what fever, shivering, work of breathing and sepsis change. A cardiac index inside the population range alongside a rising lactate and a falling venous saturation is a recognised pattern, not a contradiction. Adequacy is a question about the relationship between delivery and consumption.

Is cardiac index reliable in obesity?

Less so, and the problem is the denominator. Body surface area continues to rise with weight while metabolically active mass does not, so indexing pulls the figure down for reasons that have nothing to do with the heart. There is no agreed correction. Name the surface area formula used, and follow the trend in the individual rather than the absolute against a population range.

Related calculators

References

Edwards Lifesciences. Normal Hemodynamic Parameters and Lab Values (EU master reference card). Cardiac output 4–8 L/min, cardiac index 2.5–4 L/min/m², stroke volume 60–100 mL/beat, stroke volume index 33–47 mL/m²/beat, SVR 800–1200 and SVRI 1970–2390 dyn·s·cm⁻⁵ (·m²), PVR 100–250 dyn·s·cm⁻⁵, MAP 70–105 mmHg, CVP 2–6 mmHg, PAWP 6–12 mmHg; prints MAP as “[SBP + (2 x DBP)]/3” and SVR as “MAP-RAP x 80/CO”.
West Virginia University Medicine, Surgical Intensive Care Unit. Normal Hemodynamic Parameters — Adult. An independent reference card that agrees row for row with the Edwards figures used here, and prints the resistance formulas with the 80 written out: “80 x (MAP – RAP)/CO” and “80 x (MPAP – PAWP)/CO”.
Vincent J-L, De Backer D. Circulatory shock. N Engl J Med. 2013;369(18):1726–34. Sets out the four mechanisms of shock and why a single haemodynamic number does not identify which one a patient is in.
Leach RM, Treacher DF. The pulmonary physician in critical care 2: oxygen delivery and consumption in the critically ill. Thorax. 2002;57(2):170–7. The source this site’s oxygen content and oxygen delivery pages already use for Hüfner’s constant and the delivery relation.

Not medical advice. For healthcare professionals and education. Reference intervals vary by laboratory and assay — always use your own laboratory's. Never base a dose or a treatment decision on this page alone. Full disclaimer at calcengines.com/disclaimer/