Mean Arterial Pressure (MAP) Calculator

The formula, and why it's lopsided

MAP = diastolic + (systolic − diastolic) / 3

At a normal resting heart rate, one cardiac cycle is roughly one-third systole and two-thirds diastole. Pressure is only at its peak for that first third. A time-weighted average therefore has to count the diastolic pressure twice as heavily — which is exactly what adding one-third of the pulse pressure to the diastolic does.

That's why 120/80 gives a MAP of 93.3 rather than 100. The naive midpoint overstates the real perfusion pressure by nearly 7 mmHg.

One caveat worth knowing: the one-third rule assumes a resting heart rate. At high heart rates diastole shortens far more than systole does, so the true MAP drifts upward relative to this estimate. For a resting cuff reading it's accurate enough that intensive care units use it.

Why anyone cares

Systolic and diastolic describe the peaks and troughs. MAP describes the pressure that actually drives blood through the capillaries into tissue — so it's the number that matters for whether your organs are being perfused. The kidneys are the most sensitive, and they fail first.

The widely used floor is 65 mmHg. Below that, autoregulation in the kidneys and brain starts to break down and organ injury becomes likely, which is why 65 is the standard resuscitation target in sepsis and shock. At the other end, a sustained MAP above about 110 reflects the chronic pressure load that damages arteries, kidneys and the brain over years.

Worked example

A reading of 140/90. Pulse pressure is 50, so MAP is 90 + 50/3 = 106.7 mmHg. That's "Elevated" — consistent with stage 2 hypertension on the category chart. The naive average would have said 115, overstating it by more than 8 mmHg.

Now a shock reading of 85/50: 50 + 35/3 = 61.7 mmHg. Below the 65 floor, even though a systolic of 85 might not look alarming on its own. That inversion — where MAP flags a problem the top number hides — is the reason the calculation exists.

Where MAP is misleading

It compresses two numbers into one, so it hides the shape of the waveform. An older person with stiff arteries at 170/60 has a MAP of 96.7 — technically normal — while carrying a pulse pressure of 110, which is a serious finding. Always read MAP alongside the original pair rather than instead of them.

FAQ

What's a normal MAP?

Roughly 70–100 mmHg for a healthy adult at rest. A normal 120/80 lands at 93. Values below 65 are the clinical concern; sustained values above 110 indicate the sort of chronic hypertension that causes organ damage over time.

Why do some sources use a different formula?

You'll see MAP = (2 × diastolic + systolic) / 3. It's algebraically identical — expand it and you get the same thing. Arterial lines in hospital compute the true time-weighted integral of the pressure waveform instead, which is more accurate, especially at high heart rates; the one-third rule is the cuff-based approximation.

Can I use this with a home monitor?

Yes, and many upper-arm monitors display MAP already. The usual measurement rules apply: seated and rested five minutes, back supported, arm at heart height, no talking. A wrist monitor's readings are less dependable for this because arm position affects them so strongly.

Does MAP change during exercise?

It rises, but less than systolic does — systolic can exceed 200 during hard effort while diastolic barely moves or falls slightly, so MAP climbs modestly. The one-third approximation also gets less accurate as heart rate rises, since diastole shortens disproportionately. This calculator is for resting readings.

Is this medical advice?

No. It's one line of arithmetic on numbers you provide, plus the standard reference bands. It can't tell you why your pressure is what it is. A genuinely low MAP with symptoms — dizziness, confusion, reduced urine output — is an emergency, and no calculator should be part of that decision.

Mean Arterial Pressure Calculator