The Mean Arterial Pressure (MAP) Calculator estimates the average pressure in a patient’s arteries during one cardiac cycle. Unlike the simple systolic and diastolic numbers, MAP is the single value that best reflects whether blood is reaching the organs, which is why it drives haemodynamic decisions in intensive care and the operating theatre.
How it works
MAP is not the midpoint of systolic and diastolic pressure. Because the heart spends about two-thirds of each cycle in diastole, the diastolic pressure is weighted more heavily:
MAP = DBP + ⅓ × (SBP − DBP)
which is algebraically the same as:
MAP = (SBP + 2 × DBP) ÷ 3
The term (SBP − DBP) is the pulse pressure. For a blood pressure of 120/80,
MAP = 80 + (1/3)(120 − 80) = 80 + 13.3 ≈ 93 mmHg.
Worked examples
Normal adult: BP 120/80 mmHg → MAP = 80 + (1/3 × 40) = 93 mmHg — well within normal range
Borderline perfusion concern: BP 88/50 mmHg → MAP = 50 + (1/3 × 38) ≈ 63 mmHg — below the 65 mmHg threshold, likely to prompt intervention
Hypertensive: BP 160/100 mmHg → MAP = 100 + (1/3 × 60) = 120 mmHg — above normal, indicating elevated vascular resistance
Interpretation guide
| MAP range | Interpretation |
|---|---|
| Below 60 mmHg | Critical — inadequate organ perfusion |
| 60–65 mmHg | Marginal — borderline for brain, kidneys, coronary |
| 65–100 mmHg | Normal — adequate perfusion expected |
| Above 100 mmHg | Elevated — consider hypertensive workup if sustained |
Clinical context
In the ICU and emergency setting, MAP is preferred over systolic pressure alone because it integrates the full pressure waveform. A patient can have an acceptable systolic number but a critically low MAP if diastolic pressure drops. That is why vasopressor doses are titrated to MAP targets, not systolic targets.
The 65 mmHg threshold comes from sepsis guidelines: maintaining MAP at or above 65 mmHg with fluids and vasopressors is associated with better organ outcomes in septic shock. Some patients — particularly those with pre-existing hypertension — may need higher targets (around 80 mmHg) to maintain adequate kidney perfusion. Decisions about specific targets should always rest with the clinical team, not with a calculator alone.
The formula assumes a typical resting heart rate. At very high heart rates (above about 120 bpm), diastole shortens relative to systole, making the one-third weighting progressively less precise. Invasive arterial line monitoring measures the true time-averaged MAP directly and is the gold standard when continuous, accurate values are needed. This tool is for clinical reference and education — not a substitute for clinical judgement or direct monitoring.