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MasterMath

Mean Arterial Pressure Calculator

Mean arterial pressure and pulse pressure from the two numbers on your monitor. The mean is not the average of the two, and here you can see why.

Mean arterial pressure

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Mean arterial pressure—
Pulse pressure—
The simple average would be—
Your reading—
How it works out—
Usual reference—

How this was worked out

    Indicative result. A single reading does not diagnose hypertension. That needs repeated measurements on different days under proper conditions, interpreted by a doctor.

    The formula

    MAP = diastolic + (systolic − diastolic) / 3

    Where it comes from

    Mean arterial pressure is the average pressure across the whole cardiac cycle, and it is what actually determines organ perfusion. It is not the arithmetic average of systolic and diastolic because the heart does not spend equal time in the two phases: diastole lasts roughly twice as long as systole, so diastolic counts for two thirds and systolic for one. Hence the formula, which adds a third of the difference to the diastolic.

    How to work it out by hand

    1. Subtract the diastolic from the systolic: that is the pulse pressure
    2. Divide that difference by three
    3. Add it to the diastolic
    4. The result is the mean arterial pressure

    What is worth knowing

    The formula assumes a normal heart rate, somewhere around 60 to 80 beats. With tachycardia diastole shortens far more than systole and the two-thirds proportion stops holding, so the estimate drifts. Pulse pressure, the other figure here, is interesting in its own right: when it widens beyond about 60 mmHg in an older person it usually reflects arterial stiffness.

    Frequently asked questions

    Why is it not the average of the two numbers?

    Because the heart spends twice as long in diastole as in systole. Diastolic counts for two thirds and systolic for one.

    What is mean pressure used for?

    It determines organ perfusion, which is why intensive care and anaesthesia use it more than the two separate figures.

    What is pulse pressure?

    The difference between the top and bottom numbers. Widening a lot in an older person usually indicates arterial stiffness.

    Does the formula hold at a fast heart rate?

    Less well. It assumes a normal rate; with tachycardia diastole shortens and the proportion no longer holds.

    What mean pressure is adequate?

    In an adult it usually sits between 70 and 100 mmHg, and below 60 organ perfusion is compromised.