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Mean Arterial Pressure Calculator

Find the mean arterial pressure (MAP).

Result

93.33 mmHg

How it is calculated

Mean arterial pressure is the average pressure in the arteries during one heartbeat. Because the heart spends about twice as long in diastole as in systole, the tool weights the diastolic value more: MAP = DBP + (SBP − DBP) ÷ 3. SBP is systolic and DBP is diastolic blood pressure, both in mmHg. The diastolic value must be above zero and the systolic must be higher than the diastolic; otherwise no result is shown. The answer is in mmHg, rounded to two decimals. This is the common one-third estimate, which assumes a normal resting heart rate. At fast heart rates it is less accurate, and it is not a measured value.

Worked example

A reading is 120/80 mmHg, so SBP = 120 and DBP = 80. Pulse pressure: 120 − 80 = 40. One third of that is 40 ÷ 3 = 13.33. Add it to the diastolic value: 80 + 13.33 = 93.33 mmHg. Note that the MAP sits much nearer the diastolic number than the systolic one.

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Common mistakes

  • Averaging the two numbers: (120 + 80) ÷ 2 = 100. That overstates MAP, because the arteries spend more of each beat near diastolic pressure.
  • Swapping the two readings. Systolic is the higher, top number; if it is entered as diastolic, no result is returned.
  • Using values in kPa. The fields expect mmHg, so convert first.
  • Applying the one-third formula at a very fast heart rate or in unusual conditions, where the diastole is not twice as long as systole.
  • Treating the result as a diagnosis. The number is an estimate from one reading, and what it means depends on the person and the clinical situation.

About this calculator

Mean arterial pressure approximates the average pressure driving blood through the arterial system across a full cardiac cycle, using MAP = DBP + (SBP − DBP)/3, or equivalently diastolic pressure plus one-third of the pulse pressure. The one-third weighting reflects that, at a typical resting heart rate, roughly two-thirds of the cardiac cycle is spent in diastole and only one-third in systole, so MAP sits closer to diastolic than to systolic pressure.

Critical care physicians and anesthesiologists track MAP because it better predicts organ perfusion than either systolic or diastolic pressure alone; a MAP of at least 65 mmHg is a commonly cited threshold for adequate perfusion of the brain, kidneys and other vital organs in critically ill patients. Nurses and paramedics use this quick formula at the bedside when continuous arterial line monitoring isn't available.

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