How to Calculate Mean Arterial Pressure (MAP) From BP

Mean arterial pressure (MAP) is commonly estimated as diastolic pressure plus one third of the pulse pressure. That is the same as one third of the systolic pressure plus two thirds of the diastolic pressure. It is an estimate of the average pressure driving blood through the arteries over one heartbeat.

The formula

Both of these forms give the same answer. Pulse pressure (PP) is systolic minus diastolic.

MAP = DBP + 1/3 x (SBP - DBP)
MAP = 1/3 x SBP + 2/3 x DBP
MAP = (SBP + 2 x DBP) / 3

All values are in mmHg. The first form is usually attributed to Gauer, and a 2025 paper restates it as DBP plus 0.333 times pulse pressure (Arq Bras Cardiol). The weighting toward diastole comes from the assumption that, at a normal heart rate, the heart spends more of each cycle in diastole than in systole.

This is an estimate at normal heart rates. The same paper explains that as heart rate rises, diastole shortens much more than systole does, which is why spot calculations from two numbers can drift at higher rates. When a patient has an arterial line, pressure is measured directly from the waveform. The paper describes the area under the pressure-time curve from an invasive catheter as the gold standard for calculating MAP.

Using it in NurseTools

NurseTools is an iPhone app for nurses that is coming soon to the App Store. Nothing is downloadable yet. The MAP calculator will be one of two interactive tools available at launch.

Here is how it is planned to work:

• Enter a systolic and a diastolic value.
• The result updates from those two fields.
• If the diastolic value is not lower than the systolic value, the tool explains: “Diastolic must be lower than systolic.”
• A “Formula & details” section shows the formula in use.

The tool shows the math. It does not interpret the result or recommend care. NurseTools has no account, never asks for patient data and works offline.

Worked example

This example uses made-up numbers. It is not a patient.

Blood pressure: 118/74 mmHg.

Form 1, one third systolic plus two thirds diastolic:

1. One third of 118 = 39.33.
2. Two thirds of 74 = 49.33.
3. Add: 39.33 + 49.33 = 88.67.
4. Round to one decimal place: 88.7 mmHg.

Form 2, (SBP + 2 x DBP) / 3:

1. 2 x 74 = 148.
2. 118 + 148 = 266.
3. 266 / 3 = 88.67, which rounds to 88.7 mmHg.

Check with pulse pressure: PP = 118 - 74 = 44. One third of 44 = 14.67. Add the diastolic value: 74 + 14.67 = 88.67. All three paths agree. Rounded to a whole number, this is 89 mmHg.

Limits and common pitfalls

• It is an estimate. The formula uses two spot numbers and a fixed one-third, two-thirds assumption. The 2025 paper above notes that heart rate affects how well this holds.
• Measured MAP can differ. An arterial line reads pressure directly, and its monitor can compute the mean from the waveform rather than from the two numbers. If a calculated value and a monitored value differ, they come from different methods.
• Swapping the two weights is a frequent slip. The larger weight goes with diastolic, not systolic.
• Entering the numbers in the wrong fields gives a wrong result. Systolic is the higher value. A diastolic value at or above the systolic value points to an entry error.
• Rounding. Keep the extra decimals until the last step, then round once.
• A single threshold does not fit everyone. For education only: the 2021 Surviving Sepsis Campaign guidelines recommend an initial MAP target of 65 mm Hg for adults with septic shock, rated a strong recommendation based on moderate-quality evidence (Surviving Sepsis Campaign 2021). A review of the literature says that target should be individualized, noting that the best value may be higher in older patients with atherosclerosis or earlier hypertension (Crit Care 2015). The same review describes prolonged MAP below 60 to 65 mm Hg as prolonged hypotension.

A MAP number is one input. What it means for a particular patient depends on the clinical setting, the orders in place and the facility’s protocols.