Mean arterial pressure is the average pressure driving blood into the tissues across one cardiac cycle. It is not the midpoint of the systolic and diastolic readings — the heart spends longer relaxed than contracting, so diastole is weighted twice as heavily. MAP is the number critical care uses to judge whether organs are being perfused.
- What it measures
- Average arterial pressure across one heartbeat
- Formula
- MAP = DBP + (SBP − DBP) ÷ 3
- Usual adult range
- 70–100 mmHg
- Critical care target
- At least 65 mmHg
- BP categories
- ACC/AHA 2017 classification
Formula
Standard bedside approximation (one-third pulse pressure)MAP = DBP + (SBP − DBP) ÷ 3
- SBP
- — Systolic blood pressure in mmHg
- DBP
- — Diastolic blood pressure in mmHg
- SBP − DBP
- — Pulse pressure — the gap between the two
Written out in full this is MAP = (2 × DBP + SBP) ÷ 3, which is the identical calculation. The one-third weighting assumes a resting heart rate; at high heart rates diastole shortens and the approximation drifts upward of the true mean, which is why arterial lines integrate the actual waveform rather than using this formula.
MAP Calculator examples
| Input | Result | Category |
|---|---|---|
| 112/70 — normal | 84 mmHg | Normal |
| 120/80 | 93 mmHg | Stage 1 hypertension |
| 125/78 — elevated | 94 mmHg | Elevated |
| 135/85 — stage 1 | 102 mmHg | Stage 1 hypertension |
| 145/95 — stage 2 | 112 mmHg | Stage 2 hypertension |
| 185/120 — crisis | 142 mmHg | Hypertensive crisis |
What is mean arterial pressure?
Blood pressure is not one value — it rises to a peak as the left ventricle ejects and falls to a trough as the heart refills. Mean arterial pressure is the time-weighted average of that curve, and it is the pressure that actually determines flow into an organ, because perfusion depends on the average driving pressure rather than the peak.
At a normal resting heart rate the heart spends roughly twice as long in diastole as in systole, so the average sits nearer the diastolic number. That is where the one-third rule comes from: take the diastolic and add a third of the gap between the two readings.
For a reading of 120/80, the pulse pressure is 40 mmHg, a third of that is 13.3, and the MAP is 93 mmHg — noticeably below the arithmetic midpoint of 100.
How do you calculate MAP by hand?
- 1.Subtract the diastolic from the systolic to get the pulse pressure.
- 2.Divide the pulse pressure by three.
- 3.Add that to the diastolic pressure.
For 135/85: the pulse pressure is 50, a third is 16.7, and the MAP is 101.7 — reported as 102 mmHg. The alternative arrangement, (2 × 85 + 135) ÷ 3, gives the same 101.7.
The calculator above rejects a diastolic that is not below the systolic rather than returning a number, because that combination is always a data-entry error rather than a physiological state.
What is a normal mean arterial pressure?
In a healthy adult at rest, MAP usually sits between about 70 and 100 mmHg. Below roughly 60 mmHg, perfusion of the brain, kidneys and coronary arteries starts to fail regardless of how the individual systolic and diastolic numbers look.
| MAP (mmHg) | Interpretation |
|---|---|
| Below 65 | Below the usual minimum for organ perfusion |
| 65–69 | Borderline — at the usual minimum |
| 70–100 | Normal range in a healthy adult |
| 100–109 | Above the usual range |
| 110 and above | Well above the usual range |
The Surviving Sepsis Campaign recommends an initial MAP target of 65 mmHg for adults with septic shock on vasopressors, and trials of higher targets have not shown a mortality benefit. Individual patients may need more — someone with chronic hypertension or a raised intracranial pressure may perfuse poorly at a MAP that would be adequate for someone else.
What are the ACC/AHA blood pressure categories?
The 2017 ACC/AHA guideline replaced the old prehypertension band and lowered the threshold for hypertension from 140/90 to 130/80. Categories are decided by whichever number is worse — the systolic or the diastolic, not both.
| Category | Systolic (mmHg) | Diastolic (mmHg) |
|---|---|---|
| Normal | Below 120 | and below 80 |
| Elevated | 120–129 | and below 80 |
| Stage 1 hypertension | 130–139 | or 80–89 |
| Stage 2 hypertension | 140 or higher | or 90 or higher |
| Hypertensive crisis | Above 180 | or above 120 |
This is why a reading of exactly 120/80 is classified as stage 1 hypertension rather than normal. The elevated band requires a diastolic below 80, and 80 itself falls into the 80–89 stage 1 range. It surprises people, and it is not a bug in the calculator — the guideline is written that way deliberately, because diastolic pressure carries independent risk.
A category is not a diagnosis. Hypertension is diagnosed on the average of two or more readings taken on two or more separate occasions, ideally confirmed with home or ambulatory monitoring, because white-coat and masked hypertension are both common.
What does pulse pressure tell you that MAP does not?
Pulse pressure is the systolic minus the diastolic — around 40 mmHg in a typical healthy adult. It describes the stiffness of the large arteries and the volume ejected with each beat, which MAP averages away entirely.
- A wide pulse pressure, above roughly 60 mmHg, is common with age as the aorta stiffens, and also occurs in aortic regurgitation, anaemia, thyrotoxicosis, and arteriovenous fistulae.
- A narrow pulse pressure, below roughly 25 mmHg, can indicate a low stroke volume — hypovolaemia, cardiogenic shock, aortic stenosis, or cardiac tamponade.
- In older adults, a wide pulse pressure predicts cardiovascular events independently of the systolic reading.
Two readings with the same MAP can carry very different meanings: 150/70 and 105/93 both give a MAP of about 97, but the first describes a stiff arterial tree and the second does not.
How should blood pressure be measured?
MAP inherits every error in the reading it is built from, and cuff technique is the largest source of error in outpatient blood pressure measurement.
- Sit quietly for five minutes first, feet flat, back supported, arm resting at heart level.
- Use a correctly sized cuff — one that is too small over-reads, sometimes by 10 to 20 mmHg.
- Place the cuff on bare skin, not over a sleeve, and do not talk during the measurement.
- No caffeine, exercise, or smoking in the preceding 30 minutes, and empty your bladder first.
- Take two or three readings a minute apart and average them.
Frequently asked questions
What is the MAP for a blood pressure of 120/80?
It is 93 mmHg. The pulse pressure is 40, a third of that is 13.3, and adding it to the diastolic 80 gives 93.3. That sits comfortably inside the normal 70 to 100 range, even though 120/80 is classified as stage 1 hypertension.
Why is 120/80 not classified as normal?
Under the ACC/AHA 2017 guideline, the elevated category requires a diastolic below 80. A diastolic of exactly 80 falls in the 80 to 89 range, which is stage 1 hypertension. Diastolic pressure carries independent cardiovascular risk, so it is not ignored when the systolic looks acceptable.
What is a dangerously low MAP?
Below 65 mmHg is generally treated as inadequate perfusion pressure, and below 60 mmHg risks failing to perfuse the brain, kidneys and coronary arteries. Critical care usually targets at least 65 mmHg, though patients with chronic hypertension may need a higher figure.
Why is diastolic weighted more heavily in the formula?
At a resting heart rate the heart spends roughly twice as long filling as it does ejecting, so arterial pressure sits nearer the diastolic value for most of each cycle. Weighting diastole two-thirds and systole one-third approximates that time-weighted average.
Is MAP more useful than blood pressure?
It is more useful for perfusion, which is why critical care titrates vasopressors to MAP. For outpatient cardiovascular risk, systolic and diastolic pressure are what guidelines and trials use. The two answer different questions rather than one replacing the other.
Does this formula work at any heart rate?
Only approximately. The one-third rule assumes a resting rate where diastole lasts about twice as long as systole. At tachycardic rates diastole shortens, so the true mean is higher than this formula reports. Arterial lines integrate the real waveform instead.
Sources
- 2017 ACC/AHA Guideline for the Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults — American College of Cardiology / American Heart Association, Hypertension, 2018
- Understanding Blood Pressure Readings — American Heart Association, 2024
- Surviving Sepsis Campaign Guidelines 2021 — Society of Critical Care Medicine, 2021
- High Blood Pressure — What Is High Blood Pressure? — National Heart, Lung, and Blood Institute, 2024