Cardiac Output Calculator
Cardiac output — the blood the heart pumps each minute — from heart rate and stroke volume, with the cardiac index that scales it to body size and how it compares with resting norms.
Cardiac output is heart rate × stroke volume: 70 beats a minute at 70 mL a beat is 4.
How the cardiac output calculator works
Cardiac output is heart rate × stroke volume: 70 beats a minute at 70 mL a beat is 4.9 litres a minute, about a resting adult’s whole blood volume once round every minute. Dividing by body surface area gives the cardiac index, 2.5–4 L/min/m² at rest; it can rise four- or five-fold in hard exercise, mostly through heart rate. Stroke volume is measured by echocardiography or estimated from pulse pressure.
Formula: CO = HR × SV; CI = CO ÷ BSA
Worked examples
| Inputs | Cardiac output | Note |
|---|---|---|
| 70 bpm × 70 mL | 4.9 L/min | 4.9 L/min, CI 2.72 |
| Athlete at rest: 50 bpm × 110 mL | 5.5 L/min | 5.5 L/min |
| Hard exercise: 180 bpm × 120 mL | 21.6 L/min | 21.6 L/min |
FAQFrequently asked questions
What is a normal cardiac output?
About 4–8 L/min at rest for an adult, or a cardiac index of 2.5–4 L/min/m². It rises with exercise, pregnancy, fever and anaemia, and falls in heart failure and shock.
How is stroke volume measured?
By echocardiography (the area of the outflow tract times the velocity–time integral), cardiac MRI, or invasively by thermodilution. A rough bedside estimate is pulse pressure in mmHg × 1 mL, which is what fitness watches approximate.
Why use the index rather than the output?
A small person needs less blood flow than a large one; dividing by body surface area lets one normal range serve everyone. It is the figure intensive-care units track.
Can I use this for training?
Athletes have large stroke volumes (100–120 mL), which is why their resting heart rates are low for the same output. Maximal cardiac output is a major limit on VO₂ max.
Where these figures come from
- NCBI Bookshelf — Molecular Biology of the Cell — growth kinetics and molecular conventions
- Wellcome Sanger Institute — a leading UK genomics institute
Last checked: September 2026. Formulas are the standard textbook forms; assumptions are stated on each page because they are where these models break.