Calculate cardiac index (CI) — cardiac output normalized to body size — directly from CO and body surface area (BSA), or derive BSA from height and weight using the Du Bois formula.
⚠ Educational hemodynamics tool, not diagnostic on its own — for clinical decision support and learning, not a substitute for direct hemodynamic monitoring or a qualified clinician's judgement.
❤️ Cardiac Output & BSA
Cardiac index normalizes cardiac output for body size — a better cross-patient comparison than raw CO, since a larger person normally has a higher CO.
Volume of blood the heart pumps per minute. Typical resting adult: 4–8 L/min.
Typical adult: 1.5–2.2 m². Don't have a BSA on hand? Use the BSA tab to derive it from height and weight.
📊 Cardiac Index
Cardiac Index—
Enter cardiac output and BSA to compute.
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FormulaCO ÷ BSA
CI classification—
📏 Cardiac Output, Height & Weight
No BSA on hand? Enter height and weight and we'll derive BSA using the Du Bois formula, then compute cardiac index from it.
Volume of blood the heart pumps per minute. Typical resting adult: 4–8 L/min.
Standing height in centimetres.
Body weight in kilograms.
Different accepted formulas can produce slightly different BSA and CI values.
📊 Cardiac Index
Cardiac Index—
Enter cardiac output, height, and weight to compute.
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BSA used (Du Bois)—
CI classification—
📈 Cardiac Index Reference Bands
General adult reference ranges for resting cardiac index — not diagnostic thresholds. Your most recent result (from either the Cardiac Index or BSA tab) is highlighted.
CI (L/min/m²)
Classification
What it suggests
🩺 Reading CI in Context
CI vs. raw CO. Cardiac output on its own scales with body size, so a CO that's normal for a large adult could be inadequate for a small one — CI corrects for that by dividing by BSA.
Hemodynamic shock threshold. CI ≤ 2.2 L/min/m² is one commonly used hemodynamic criterion; shock assessment also requires clinical evidence of hypoperfusion and professional evaluation.
High-output states. Sepsis, severe anemia, thyrotoxicosis, and arteriovenous fistulas can all push CI above the normal range.
BSA formulas differ. Du Bois and Mosteller can produce slightly different estimates, especially when body habitus differs from the populations used to derive the formulas.
CI is only as reliable as the CO and BSA (or height/weight) it's built from — recheck those inputs first if a result looks unexpected.
4 min read4 steps6 terms3 examples6 FAQsCI (L/min/m²) = CO (L/min) ÷ BSA (m²)
Cardiac index takes the single most important number in hemodynamics — how much blood the heart pumps per minute — and corrects it for the one variable that makes raw comparisons misleading: body size.
Use the Cardiac Index tab when you already know body surface area (BSA) — from a lab report, chart, or the dedicated BSA calculator. Use the BSA tab when you only have height and weight; it derives BSA via the Du Bois formula before computing cardiac index.
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Enter your values
The Cardiac Index tab needs cardiac output (CO) in L/min and BSA in m². The BSA tab needs CO plus height in centimetres and weight in kilograms. Both tabs update instantly as you type.
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Read the result and its band
The headline shows cardiac index in L/min/m², with a colour-coded classification: Cardiogenic shock range, Borderline low, Normal (2.5-4.0 L/min/m²), or High. The interpretation line spells out whether the value falls inside the normal range.
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Check the Normal Range tab
Open the Normal Range tab for the full reference table — your most recent result from either tab is highlighted — plus context on why CI is preferred over raw cardiac output. Use Share or Copy to save a reading; your numbers are encoded in the URL.
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Reference
Formula & Methodology
2 formulas▸
Cardiac index
CI (L/min/m²) = CO (L/min) ÷ BSA (m²)
Cardiac index normalizes cardiac output for body size by dividing it by body surface area. Unlike the Fick cardiac-output equation, there is no unit-conversion factor here — CO in L/min divided by BSA in m² already returns L/min/m² directly. Example: CO 5 L/min ÷ BSA 1.8 m² = 2.78 L/min/m².
The classic 1916 reference formula for estimating body surface area from height and weight, used when a direct BSA measurement isn't available. It remains widely cited but tends to slightly underestimate BSA in people with obesity — see the dedicated BSA calculator to compare it against four other formulas.
The Cardiac Index Calculator applies CI = cardiac output CO (L/min) ÷ body surface area BSA (m²), directly if BSA is provided or after deriving BSA from height and weight via the Du Bois formula (BSA = 0.007184 × weight_kg^0.425 × height_cm^0.725, Arch Intern Med 1916). Interpretation bands (CI < 2.2 cardiogenic shock range, 2.2-2.5 borderline low, 2.5-4.0 normal, > 4.0 high L/min/m²) are general adult reference ranges drawn from standard cardiovascular physiology references, not patient-specific diagnostic thresholds.
Assumption: Cardiac output and BSA (or height/weight) are entered for the same patient at the same point in time.
Assumption: Body surface area must be a positive value greater than zero; a zero or negative BSA cannot be resolved into a valid cardiac index.
Assumption: The user wants a screening estimate and interpretation context, not a diagnosis, treatment plan, or dosing decision.
Limitations & guidance
This calculator performs the arithmetic only and cannot validate the accuracy of user-entered cardiac output, BSA, height, or weight.
Interpretation bands are general adult reference ranges; actual targets vary by patient condition and care setting.
Du Bois is one of several validated BSA formulas and can differ from alternatives (e.g. Mosteller) by a few percent — this tool does not offer a formula choice like the dedicated BSA calculator does.
This tool does not diagnose, monitor, or guide treatment of any condition. Do not make medical decisions based on its output.
A cardiac index at or below approximately 2.2 L/min/m² is one hemodynamic criterion used in cardiogenic-shock definitions. Interpretation requires clinical evidence of hypoperfusion and professional assessment. Seek emergency care for severe shortness of breath, chest pain, fainting, confusion, cold or mottled skin, very low blood pressure, or rapidly worsening symptoms.
Results depend on the accuracy, timing, and measurement method of the inputs. Do not change medication, fluid, exercise, or treatment decisions based solely on this calculator. Discuss unexpected or borderline results with a qualified healthcare professional.
Professional guidance: The Cardiac Index Calculator is for health education and clinical decision support only. It provides an estimate based on user-entered values, not medical advice, diagnosis, treatment, or a substitute for direct hemodynamic monitoring or care from a licensed healthcare professional. Always rely on a qualified clinician for medical decisions.
Cardiac index (CI)Cardiac output divided by body surface area (CO ÷ BSA), expressed in L/min/m². Normal resting adult CI is roughly 2.5-4.0 L/min/m².
Body surface area (BSA)The total surface area of the human body, expressed in square metres (m²). Used to normalize cardiac output, drug dosing, and other physiologic measures for body size. Typical adult BSA: 1.5-2.2 m².
Du Bois formulaThe 1916 BSA equation (0.007184 × weight_kg^0.425 × height_cm^0.725), the historical reference standard for estimating body surface area from height and weight.
Cardiogenic shockA state of critically inadequate cardiac output relative to the body's needs, typically caused by severe heart muscle dysfunction. A cardiac index well under 2.2 L/min/m² is consistent with cardiogenic shock and needs urgent evaluation.
HemodynamicsThe study of blood flow and the forces (pressure, resistance, flow) that govern it within the cardiovascular system.
Normal rangeFor cardiac index, the general adult reference range of 2.5-4.0 L/min/m² at rest. Values above or below this range prompt further clinical evaluation, but are not a diagnosis on their own.
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Scenarios
Real-World Examples
3 worked examples▸
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Resting adult — direct BSA entry
Cardiac Index tab, CO 5 L/min, BSA 1.8 m²
Cardiac output 5 L/minBody surface area 1.8 m²Cardiac index 2.78 L/min/m²
CI = 5 ÷ 1.8 = 2.78 L/min/m², comfortably inside the normal 2.5-4.0 L/min/m² range for a resting adult. This pairs with a cardiac output of 5 L/min for a typical-sized patient.
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Cardiogenic shock warning sign
Cardiac Index tab, CO 3.5 L/min, BSA 1.75 m²
Cardiac output 3.5 L/minBody surface area 1.75 m²Cardiac index 2.00 L/min/m²
CI = 3.5 ÷ 1.75 = 2.00 L/min/m² — below the 2.2 L/min/m² cardiogenic shock threshold, even though the raw cardiac output of 3.5 L/min might not look alarming on its own. This is exactly why clinicians prefer CI over raw CO: it accounts for body size. A reading this low warrants urgent clinical evaluation.
Du Bois BSA for 178 cm / 84 kg is about 2.02 m². CI = 6 ÷ 2.02 = 2.97 L/min/m² — normal, in the upper half of the 2.5-4.0 range. The BSA tab is useful whenever a direct BSA figure isn't already charted.
Cardiac index takes the single most important number in hemodynamics — how much blood the heart pumps per minute — and corrects it for the one variable that makes raw comparisons misleading: body size. A cardiac output that looks perfectly normal for a large adult could actually represent inadequate perfusion in a smaller person, and vice versa. This guide explains why CI normalizes for body size, how to get body surface area (BSA) two different ways, and how to read a CI result against the standard normal range and the cardiogenic shock threshold.
CI vs. raw cardiac output — why normalize to body size
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Cardiac output (CO) scales with body size: larger people generally need — and have — a higher absolute CO to perfuse more tissue. That makes raw CO a poor metric for comparing across patients, or for judging whether a given CO is actually adequate for a specific person. Cardiac index solves this by dividing CO by body surface area (BSA), producing a size-normalized figure in L/min/m² that's directly comparable across patients of very different sizes.
This is the same logic behind why clinicians reach for cardiac index rather than cardiac output when assessing whether perfusion is adequate: a CO of 4.5 L/min might be entirely normal for a petite adult but borderline-low for a much larger one. Cardiac index accounts for that difference automatically.
Two ways to get BSA: direct entry vs. Du Bois
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If BSA is already known — from a chart, lab report, or a prior calculation — enter it directly on the Cardiac Index tab. Otherwise, the BSA tab derives it from height and weight using the Du Bois formula (BSA = 0.007184 × weight_kg^0.425 × height_cm^0.725), the classic 1916 reference equation still widely used in clinical practice today.
Du Bois is one of several validated BSA formulas — Mosteller, Haycock, and Gehan-George are common alternatives that can differ from Du Bois by a few percent, particularly at the extremes of body weight. The dedicated BSA calculator lets you compare all five side by side; this calculator uses Du Bois for consistency with the most commonly cited cardiac index literature.
Reading CI against the normal range and the cardiogenic shock threshold
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A typical resting adult cardiac index falls between 2.5 and 4.0 L/min/m². Values between 2.2 and 2.5 are borderline low and worth watching. A cardiac index well under 2.2 L/min/m² is consistent with cardiogenic shock — a state of critically inadequate perfusion relative to the body's needs — and calls for urgent clinical evaluation, not a wait-and-see approach.
On the high end, sepsis, severe anemia, thyrotoxicosis, and arteriovenous fistulas can all push cardiac index above the normal range as the body compensates for reduced oxygen-carrying capacity or peripheral vasodilation. As with cardiac output, this calculator is an educational and screening aid — it does not diagnose or replace direct hemodynamic monitoring by a qualified clinician.
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Questions
Frequently Asked Questions
6 questions▸
What is a normal cardiac index?+
A typical resting adult cardiac index falls between 2.5 and 4.0 L/min/m². Values between 2.2 and 2.5 L/min/m² are considered borderline low, and anything above 4.0 L/min/m² is classified as high in this calculator.
What is the cardiogenic shock cutoff for cardiac index?+
A cardiac index well under 2.2 L/min/m² is consistent with cardiogenic shock — a state of critically inadequate blood flow relative to the body's needs — and warrants urgent clinical evaluation. This calculator flags such values but does not diagnose the underlying cause.
What formula does this calculator use for BSA?+
The BSA tab uses the Du Bois formula (BSA = 0.007184 × weight_kg^0.425 × height_cm^0.725), the classic 1916 reference equation. If you already know your BSA from another source, you can skip this and enter it directly on the Cardiac Index tab.
Why divide cardiac output by body surface area?+
Cardiac output scales with body size, so comparing raw CO across patients of different sizes can be misleading. Dividing by BSA produces cardiac index, a size-normalized figure in L/min/m² that lets clinicians judge whether blood flow is adequate for a specific person rather than for an average-sized adult.
What units does this calculator use?+
Cardiac index is reported in litres per minute per square metre (L/min/m²). Cardiac output is entered in L/min, body surface area in m², height in centimetres, and weight in kilograms.
How is cardiac index related to cardiac output?+
Cardiac index is cardiac output divided by body surface area (CI = CO ÷ BSA). If you already have your cardiac output figure, the dedicated Cardiac Output Calculator computes it from stroke volume and heart rate, or via the Fick method — its result feeds directly into this calculator.
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