By Zencalcy Editorial TeamLast reviewed About us
Systemic vascular resistance estimates how much the systemic circulation resists blood flow. It is calculated from the pressure drop across the circulation and the cardiac output, with a conversion factor that gives dynes·s·cm⁻⁵. This calculator returns the resistance and places it against the usual reference range.
Afterload estimate from pressure, filling and flow.
SVR = (MAP − CVP) ÷ CO × 80
The pressure difference drives flow and the resistance opposes it. The factor 80 converts mmHg·min/L into dynes·s·cm⁻⁵. A value of roughly 800–1200 dynes·s·cm⁻⁵ is commonly cited as normal, with lower values suggesting vasodilation and higher values vasoconstriction or a low-output state.
| Symbol | Meaning |
|---|---|
| MAP | Mean arterial pressure in mmHg. |
| CVP | Central venous pressure in mmHg. |
| CO | Cardiac output in litres per minute. |
| SVR | Systemic vascular resistance in dynes·s·cm⁻⁵. |
The pressure gradient is 90 − 5 = 85 mmHg. SVR = 85 ÷ 5 × 80 = 1,360 dynes·s·cm⁻⁵, above the usual range. With MAP 70, CVP 2 and CO 6, the result is 68 ÷ 6 × 80 = 906.7 dynes·s·cm⁻⁵, within the usual range.
The circulation can be modelled like an electrical circuit, with pressure as voltage, flow as current and resistance as the ratio between them. That analogy makes the formula intuitive, but it also hides assumptions. The model treats the circulation as a single tube with steady flow, while real blood flow is pulsatile and distributed across parallel beds. Mean arterial pressure is itself a calculated value, and central venous pressure is an imperfect downstream estimate. Despite these simplifications, the resistance estimate is useful because it separates flow from pressure. A patient with a normal blood pressure may have a low output and a very high resistance, or a high output and a low resistance. Seeing those patterns helps clinicians reason about vasoactive support and fluid status, provided the numbers are read together with perfusion and the trend over time.
Continue with the Mean Arterial Pressure Calculator, Pulse Pressure Calculator, or the QTc Calculator — or browse more cardiology tools and all health calculators.
It represents the combined resistance of the systemic arterioles and capillaries to blood flow. It is a derived estimate rather than a direct measurement, and it changes with vasoactive drugs, sepsis, temperature and other states.
Blood pressure, ECG and risk scores are screening aids, not diagnoses. A single reading can be misleading; trends and proper technique matter. Scores estimate population risk and do not replace clinical assessment, anticoagulation decisions or emergency care.
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Last reviewed: September 2026. See how we build and check every tool on the about page.
Content updated: September 2026