Cardiac Index Calculator (cardiac output ÷ body surface area)

Understanding the cardiac index calculator — concept and principle

This calculator works out the cardiac index, cardiac output divided by body surface area, so that heart output can be compared between people of different sizes. It also gives the body surface area (Mosteller) and, with a heart rate, the stroke volume and stroke volume index. Intensive-care and cardiology staff and students use it.

Output scaled to body size — with the default inputs: 2.8 L/min/m².

How it is calculated

Body surface area BSA (Mosteller) = √(height (cm) × weight (kg) ÷ 3,600)
Cardiac index CI = cardiac output (L/min) ÷ BSA
Stroke volume = cardiac output × 1,000 ÷ heart rate
Stroke volume index = stroke volume ÷ BSA
Usual resting adult ranges: CI 2.5–4.0 L/min/m²; stroke volume index about 33–47 mL/m² per beat

The principle

A large person needs more blood flow than a small one, so cardiac output alone cannot be compared across people. Dividing by body surface area normalises it. The Mosteller formula is a simple, widely used estimate of surface area. Stroke volume, the blood ejected per beat, separates the effect of heart rate from the pumping of each beat. A low index can come from a weak heart, low blood volume or a slow rhythm.

Worked example

Defaults: cardiac output 5.2 L/min, height 172 cm, weight 72 kg, heart rate 70.

BSA = √(172 × 72 ÷ 3,600) = √3.44 = 1.85 m².
CI = 5.2 ÷ 1.855 = 2.8 L/min/m²: Within the usual range.
Stroke volume = 5,200 ÷ 70 = 74 mL; stroke volume index = 74.3 ÷ 1.855 = 40 mL/m².

Each point is the calculator re-run with only “Cardiac output (L/min)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Cardiac output (L/min)	Cardiac index (L/min/m²)
1.3	0.7
2.6	1.4
3.9	2.1
5.2	2.8
6.5	3.5
7.8	4.21
10.4	5.61

How to read the result

Where does your result fall?

A cardiac index within 2.5–4.0 is typical at rest. Values must be read with blood pressure, filling pressures, lactate and the clinical picture; a normal index does not rule out problems, and the method used to measure cardiac output affects accuracy.

Common mistakes

Using weight in pounds or height in inches in the Mosteller formula.
Comparing an index measured during exercise with resting ranges.
Ignoring measurement method differences (thermodilution, echocardiography, pulse contour).
Reading the index without the clinical context.

Keep in mind: Not a diagnosis. Haemodynamic values are interpreted by clinicians with full monitoring.

Frequently asked questions

What is a normal cardiac index?

About 2.5–4.0 L/min/m² at rest in adults.

Why divide by body surface area?

To compare heart output between people of different sizes.

What is stroke volume?

The volume of blood pumped with each heartbeat, typically 60–100 mL at rest.

Sources: Edwards Lifesciences Clinical Education, "Normal Haemodynamic Parameters and Laboratory Values" (2022)

Checked 9 Nov 2026. Edwards Lifesciences Clinical Education, “Normal Haemodynamic Parameters and Laboratory Values” (2022, PP--EU-4269 v1.0): CI = CO/BSA, 2.5–4 L/min/m²; CO 4–8 L/min; SV = CO/HR × 1000, 60–100 mL; SVI 33–47 mL/m²/beat. BSA by the Mosteller formula (standard).

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