How to Calculate Mean Arterial Pressure (MAP), With a Worked Example
Mean arterial pressure (MAP) is the average pressure in the arteries across one full cardiac cycle. The formula is MAP = (SBP + 2 x DBP) / 3. It matters more than the systolic or diastolic number alone because it is what actually determines how well blood reaches organs like the kidneys and brain. A normal MAP sits between about 70 and 100 mmHg.
The formula
MAP = (SBP + 2 x DBP) / 3, which is the same as DBP + (SBP - DBP) / 3. Both versions give the same number; the second one just makes it clearer that you’re starting from diastolic and adding a third of the pulse pressure on top.
Diastolic pressure gets counted twice because of how time is split across a cardiac cycle. At a normal resting heart rate, the heart spends roughly two-thirds of each cycle in diastole (the relaxed, filling phase) and only a third in systole (the contraction that produces the systolic peak). MAP is a time-weighted average, not a simple average of the two extremes, so diastolic pressure dominates it the same way it dominates the clock.
A normal MAP runs about 70 to 100 mmHg. That range holds for most healthy adults at rest, and it’s the reference band clinicians check a reading against before deciding whether perfusion looks adequate.
Worked example
Take a standard reading of 120/80 mmHg (SBP 120, DBP 80).
MAP = (120 + 2 x 80) / 3 = (120 + 160) / 3 = 280 / 3 = 93.3, which rounds to 93 mmHg.
| Value | Calculation | Result |
|---|---|---|
| MAP | (120 + 2x80) / 3 | 93 mmHg |
| Pulse pressure | 120 - 80 | 40 mmHg |
That 93 mmHg sits comfortably inside the 70 to 100 mmHg normal band. Pulse pressure, the simple difference between systolic and diastolic (40 mmHg here), is a different number worth knowing alongside MAP: it reflects arterial stiffness and stroke volume rather than perfusion, but it’s easy to confuse with MAP since both come from the same two inputs.
Calculate it with your own values
Why 65 mmHg matters
A MAP of about 65 mmHg or higher is the commonly cited minimum target for adequate organ perfusion. It shows up most concretely in the Surviving Sepsis Campaign guidance, where 65 mmHg is the resuscitation target clinicians titrate vasopressors to in septic shock. Below that line, organs (kidneys especially) are at rising risk of not getting enough blood flow to function.
Take a hypotensive patient with a reading of 88/52 mmHg, the kind of number you’d see in septic shock before or during vasopressor titration.
Correct MAP = (88 + 2 x 52) / 3 = (88 + 104) / 3 = 192 / 3 = 64 mmHg. That’s below 65, meaning this patient is under-resuscitated and needs escalated vasopressor support.
Now compare that to the shortcut some people reach for: just averaging systolic and diastolic like a normal mean, (88 + 52) / 2 = 70 mmHg. That naive number sits above 65 and wrongly suggests the patient is already adequately perfused. The real, correctly weighted MAP says otherwise.
| Method | Calculation | Result | Reads as adequate (>=65)? |
|---|---|---|---|
| Correct MAP formula | (88 + 2x52) / 3 | 64 mmHg | No |
| Naive average (wrong) | (88 + 52) / 2 | 70 mmHg | Yes, incorrectly |
A 6 mmHg gap between the two methods, and it crosses the 65 threshold in exactly the wrong direction, in exactly the scenario, borderline hypotension, where that difference changes what happens next. Use the naive average here and you might hold off on escalating support for a patient who actually needs it.
The 65 mmHg figure is a population-level minimum, not a universal number for every patient. A chronically hypertensive patient’s organs are used to running at a higher baseline pressure, so they may need a MAP above 65, sometimes well above it, to maintain the same perfusion they’re accustomed to. The target still has to be individualized.
Common mistakes
Averaging systolic and diastolic instead of using the weighted formula. This is the mistake worth watching for most closely, and the 88/52 example above shows exactly why: the naive average can land on the wrong side of the 65 mmHg threshold in precisely the situation where that threshold drives a treatment decision. Always use (SBP + 2 x DBP) / 3, never a plain average of the two numbers.
Trusting a single cuff reading in shock or arrhythmia. Cuff-based blood pressure, and the MAP formula built on it, assumes a roughly 1:2 systole:diastole time ratio. That ratio holds at normal heart rates but breaks down with tachycardia, where diastole shortens disproportionately more than systole. In critically ill or tachycardic patients, a continuous arterial line, which integrates the actual pressure waveform rather than estimating from two cuff numbers, is the more reliable source.
Treating one MAP reading as a trend. A single number is a snapshot. Whether MAP is climbing toward target or drifting down matters as much as where it sits right now, especially during active resuscitation or vasopressor titration.
Assuming 65 mmHg applies identically to every patient. It’s a reasonable default minimum, not a fixed rule. Chronic hypertension, baseline organ function, and the clinical picture all shift what “adequate” actually means for a given patient.
Frequently asked questions
What is the formula for mean arterial pressure?
MAP = (SBP + 2 x DBP) / 3, equivalently DBP + (SBP - DBP) / 3. Plug in systolic and diastolic pressure in mmHg and the result is MAP in mmHg.
Why does diastolic blood pressure count twice in the formula?
Because at a normal resting heart rate, the heart spends roughly two-thirds of each cardiac cycle in diastole and only a third in systole. MAP is a time-weighted average of pressure across the cycle, so diastolic pressure, which holds for the longer phase, carries twice the weight of systolic pressure in the calculation.
What counts as a normal MAP, and what’s the critical 65 mmHg threshold?
A normal MAP for a healthy adult at rest is roughly 70 to 100 mmHg. Separately, about 65 mmHg is the commonly cited minimum needed for adequate organ perfusion, used as the resuscitation target in conditions like septic shock. A MAP below 65 signals a perfusion problem; a MAP inside 70 to 100 signals a normal, healthy reading. The two numbers answer different questions, one is “what’s typical,” the other is “what’s the floor before organs are at risk.”
Does a fast heart rate (tachycardia) affect how accurate the MAP formula is?
Yes. The formula assumes a roughly 1:2 ratio between time spent in systole and diastole, which holds at normal heart rates. As heart rate rises, diastole shortens disproportionately more than systole, so the ratio the formula assumes no longer matches reality and the estimate gets rougher. In critically ill or tachycardic patients, continuous arterial line monitoring, which measures the real pressure waveform instead of estimating from a cuff reading, is preferred over the formula.