Cardiac Output & Cardiac Index Calculator

Background.

Cardiac output is the volume of blood the heart pumps each minute, and it is the single most fundamental number in hemodynamics: every organ in the body depends on it for oxygen delivery, and nearly every drug used in critical care — vasopressors, inotropes, diuretics, vasodilators — is titrated with one eye on how it moves this number. This calculator computes cardiac output (CO) from heart rate and stroke volume, and cardiac index (CI) by normalizing CO to body surface area (BSA), using the same stroke-volume method taught in every physiology curriculum and used at the bedside whenever a clinician already has a measured stroke volume from echocardiography, thermodilution, or a pulmonary artery catheter.

This tool is an educational estimate, not a diagnostic device, and it does not replace clinical judgment. It performs one multiplication and one division on the numbers you provide; it has no way to know whether your stroke volume was measured accurately, whether your heart rhythm is regular enough for the number to be meaningful beat-to-beat, or whether a low or high result reflects genuine cardiac dysfunction versus a normal physiological response to fever, anemia, pregnancy, or exercise. Any cardiac output or cardiac index value obtained here — or anywhere else — should be interpreted by a qualified clinician in the context of the full clinical picture, not treated as a standalone diagnosis.

The formula itself is simple: cardiac output equals heart rate multiplied by stroke volume, divided by 1000 to convert the stroke volume's usual unit (milliliters) into liters so the result reads in the conventional liters-per-minute. A resting adult with a heart rate of 70 beats per minute and a stroke volume of 70 milliliters has a cardiac output of 4.9 liters per minute — enough to recirculate the body's entire blood volume roughly once every minute. Because a five-foot, 100-pound adult and a six-foot-six, 280-pound adult can have identical raw cardiac outputs while having very different metabolic demands, clinicians almost always look at cardiac index rather than raw cardiac output: dividing CO by body surface area produces a size-normalized number that is comparable across patients of any build. If you only know height and weight rather than BSA directly, run those numbers through Quanta's Body Surface Area calculator first (it computes BSA via the Mosteller formula by default, alongside Du Bois, Haycock, Boyd, and Gehan-George) and carry the resulting square-meter figure over here.

Cardiac output and cardiac index are used constantly in intensive care, cardiac surgery, cardiology consultation, and exercise physiology — to titrate inotropic support after cardiac surgery, to distinguish cardiogenic shock from other shock states, to guide fluid resuscitation, and to quantify how much a trained athlete's stroke volume adapts compared to a sedentary person's. This calculator gives you the arithmetic instantly so you can focus on interpreting the number rather than computing it, but the interpretation itself — what a given CO or CI means for a specific patient — is a clinical judgment that belongs with a treating clinician, not with a web calculator.

What is cardiac output & cardiac index calculator?

Cardiac output (CO) is the volume of blood the left ventricle ejects into the systemic circulation per minute, conventionally reported in liters per minute (L/min). It is the product of two independently regulated quantities: heart rate (HR), the number of times the heart beats per minute, and stroke volume (SV), the volume of blood ejected with each individual beat. Stroke volume itself is governed by preload (how much blood fills the ventricle before contraction, tied to venous return), afterload (the resistance the ventricle must pump against, largely set by systemic vascular resistance and arterial pressure), and contractility (the intrinsic strength of the heart muscle's contraction, which can be enhanced by inotropic drugs or reduced by heart failure).

Cardiac index (CI) is cardiac output divided by body surface area (BSA), expressed in liters per minute per square meter (L/min/m²). Because larger bodies generally need more total blood flow to meet metabolic demand, comparing raw cardiac output across patients of very different sizes can be misleading; indexing to BSA removes that size effect and is the number clinicians actually chart and trend. In healthy resting adults, cardiac output typically falls between 4 and 8 L/min, averaging around 5 L/min, and cardiac index typically falls between 2.5 and 4.0 L/min/m² (StatPearls, Physiology, Cardiac Index). Both figures rise substantially during exercise, pregnancy, fever, and anemia, and fall in cardiogenic shock, severe heart failure, and some arrhythmias — but a single number in isolation cannot distinguish between these causes, which is why cardiac output and cardiac index are always interpreted alongside blood pressure, heart rhythm, filling pressures, and the rest of the clinical exam.

How to use this calculator.

1. 01Enter the heart rate in beats per minute — from a monitor, pulse check, or ECG strip.
2. 02Enter the stroke volume in milliliters — typically obtained from echocardiography (Simpson's method or velocity-time integral), thermodilution via a pulmonary artery catheter, or the Fick method. Normal resting values in healthy adults run 60-100 mL.
3. 03Enter the body surface area in square meters. If you only have height and weight, calculate BSA first with Quanta's Body Surface Area calculator, then bring that number here.
4. 04Read the primary result, cardiac output in L/min, and the cardiac index in L/min/m² beneath it.
5. 05Check the range labels under each result — they show whether the value sits within, below, or above the typical resting range cited from StatPearls.
6. 06Interpret the numbers together with heart rate, blood pressure, and the rest of the clinical picture — a single CO or CI value out of context does not diagnose anything on its own; bring the result to a clinician for interpretation.

The formula.

Cardiac output is derived from first principles: if the heart ejects a stroke volume SV with every beat, and it beats HR times per minute, then the total volume pumped per minute is simply HR × SV. Stroke volume is conventionally measured in milliliters, so the raw product HR × SV is in milliliters per minute; dividing by 1000 converts it to liters per minute, the unit clinicians actually use. This is the stroke-volume method of computing cardiac output, distinct from the Fick method, which instead derives CO from oxygen consumption divided by the arteriovenous oxygen content difference (CO = VO2 / (a-v O2 difference)) — the two methods should agree closely when stroke volume is measured accurately, and clinicians sometimes cross-check one against the other.

Cardiac index simply divides the cardiac output figure by body surface area: CI = CO / BSA. Because the equation is a straight division, doubling BSA while holding CO fixed halves the index — which is exactly the intuition clinicians rely on when comparing a small-framed patient to a large-framed one. BSA itself is not a directly measurable quantity; it is estimated from height and weight using regression formulas such as Mosteller's BSA = √(height_cm × weight_kg ÷ 3600), which is why this calculator asks for BSA as an input rather than recomputing it internally — pairing this tool with Quanta's dedicated Body Surface Area calculator keeps each calculation auditable on its own terms and lets you switch between the five standard BSA formulas (Mosteller, Du Bois, Haycock, Boyd, Gehan-George) without duplicating that logic here.

The normal reference ranges used by this calculator — 4 to 8 L/min for cardiac output and 2.5 to 4.0 L/min/m² for cardiac index — come from StatPearls' Physiology, Cardiac Index chapter (Patel et al., 2024), a peer-reviewed clinical reference hosted on the NCBI Bookshelf. These are population reference ranges for a resting adult, not diagnostic thresholds: an athlete's resting cardiac index sits comfortably within the normal band even though their heart achieves it with a much larger stroke volume and a much lower heart rate than a deconditioned adult, and a febrile or pregnant patient's cardiac output rises above the typical resting range as a normal physiological response rather than a pathological one. Values well below the normal range — particularly a cardiac index under roughly 2.2 L/min/m² with hemodynamic support or under 1.8 L/min/m² without it — raise concern for cardiogenic shock in the appropriate clinical context, but that determination always requires a clinician weighing the number alongside blood pressure, mentation, urine output, and lactate, not the number alone.

A worked example.

Frequently asked questions.

References& sources.

1. [1]King J, Lowery DR. Physiology, Cardiac Output. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; updated July 17, 2023.
2. [2]Patel N, Durland J, Awosika AO, Makaryus AN. Physiology, Cardiac Index. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; updated June 8, 2024.
3. [3]Khalil B, Foster C, Launico MV. Physiology, Stroke Volume. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; updated June 19, 2026.