Mean Arterial Pressure
MAP from a blood pressure reading, with the pulse pressure it is built from.
Pulse pressure 40 mmHg · reported as 120/80
Mean arterial pressure is the average pressure pushing blood through the organs across one cardiac cycle. Calculate it as MAP = DBP + ⅓(SBP − DBP). A reading of 120/80 mmHg gives a pulse pressure of 40 and a MAP of about 93 mmHg, inside the usual 70–100 range.
Why the diastolic counts twice
MAP is not the midpoint between the two numbers, and the reason is timing. At a normal heart rate the heart spends roughly a third of each cycle in systole and two thirds in diastole, so the lower pressure is present for twice as long. Weighting it accordingly gives the time-averaged pressure, which is what perfusion actually depends on — an organ is fed by the pressure it sees over the whole cycle, not by the brief peak.
That is why MAP, rather than systolic pressure, is the number watched in critical care. Two patients can share a systolic of 100 and have quite different mean pressures, and it is the mean that determines whether the kidneys, brain and gut are being perfused.
The two formulas are the same formula
MAP is written either as DBP + ⅓(SBP − DBP) or as (SBP + 2 × DBP) ÷ 3. They are algebraically identical and always give the same answer; the first makes the reasoning visible, while the second is quicker to run in your head. Both assume a normal heart rate, and both drift from the true mean in marked tachycardia, where diastole shortens and the real average rises above the estimate.
SBP systolic, DBP diastolic, both in mmHg; the bracketed term is the pulse pressure
- 1 Find the pulse pressure. Subtract diastolic from systolic: for 120/80, that is 120 − 80 = 40 mmHg.
- 2 Take one third of it. 40 ÷ 3 = 13.3 mmHg.
- 3 Add that to the diastolic. 80 + 13.3 = 93.3 mmHg, so the MAP is about 93 mmHg.
- 4 Check it the other way if you like. (120 + 2 × 80) ÷ 3 = 280 ÷ 3 = 93.3 mmHg — the same number.
- 5 Read it against the thresholds. 93 mmHg sits inside the usual 70–100 mmHg range and comfortably above the 65 mmHg commonly cited as the lower limit for organ perfusion.
Worked examples
Rounded to the nearest mmHg. Pulse pressure is the gap the formula weights.
| Blood pressure | Pulse pressure | MAP |
|---|---|---|
| 120/80 | 40 mmHg | 93 mmHg |
| 110/70 | 40 mmHg | 83 mmHg |
| 90/60 | 30 mmHg | 70 mmHg |
| 85/50 | 35 mmHg | 62 mmHg |
| 140/90 | 50 mmHg | 107 mmHg |
| 100/40 | 60 mmHg | 60 mmHg |
What the numbers are usually measured against
A MAP of roughly 70–100 mmHg is the range normally quoted for an adult at rest, and about 60–65 mmHg is the pressure generally taken as the minimum needed to perfuse the major organs. The Surviving Sepsis Campaign recommends an initial target of 65 mmHg for adults with septic shock on vasopressors — a recommendation carried unchanged into its 2026 guideline, which adds a conditional range of 60–65 mmHg for adults aged 65 and over.
Two cautions belong with any hand-calculated MAP. The formula is an estimate built on a normal heart rate, so an arterial line — which integrates the actual pressure waveform — is the more reliable figure when one is in place. And the last row of the table is the reason MAP is never read alone: 100/40 and 90/60 produce similar means from very different haemodynamics, so the trend, the pulse pressure and the patient matter alongside the number. Interpretation and any change in therapy belong to a qualified professional working to local protocol.