Mean Arterial Pressure Calculator
Calculate MAP, pulse pressure, and estimate cardiac output from blood pressure measurements.
Why MAP Is Not the Average of Systolic and Diastolic
The heart spends roughly two thirds of each cardiac cycle in diastole and only one third in systole. A simple average would weight the two equally and overestimate the true mean pressure, so the formula weights diastole double.
For 120/80 this gives 93.3 mmHg, whereas the arithmetic mean would give 100 — a 7 mmHg overestimate. That matters because MAP, not systolic pressure, drives organ perfusion.
One caveat: the one-third approximation assumes a normal heart rate. At tachycardia diastole shortens disproportionately, so MAP moves closer to the arithmetic mean and the formula progressively underestimates.
Why Clinicians Watch MAP
| MAP (mmHg) | Interpretation |
|---|---|
| < 60 | Organ perfusion compromised |
| ≥ 65 | Standard resuscitation target in sepsis |
| 70–100 | Normal range |
| > 110 | Sustained elevation — end-organ risk |
The 65 mmHg threshold appears throughout critical care because below roughly that pressure, autoregulation in the kidney and brain fails and perfusion becomes directly pressure-dependent. A patient can have an acceptable systolic reading and still be under-perfusing if diastolic pressure is very low.
Pulse Pressure Carries Separate Information
| Pulse pressure | Suggests |
|---|---|
| < 25 mmHg | Narrow — low stroke volume, shock, tamponade |
| 30–60 mmHg | Normal |
| > 60 mmHg | Wide — arterial stiffening, aortic regurgitation, thyrotoxicosis |
Pulse pressure reflects stroke volume and arterial compliance. Widening with age is largely arterial stiffening, and in older adults it predicts cardiovascular risk better than systolic pressure alone.
Worked Examples
Common Mistakes
Diastole occupies about two thirds of the cycle, so it is weighted double. The arithmetic mean overestimates MAP by several mmHg.
Diastole shortens disproportionately with tachycardia, so the one-third approximation progressively underestimates MAP.
Organ perfusion depends on MAP. A patient with an acceptable systolic reading but very low diastolic pressure can still be under-perfusing.
A narrow pulse pressure suggests low stroke volume and can be an early sign of shock before MAP falls appreciably.