MAP Calculator (Mean Arterial Pressure)
Mean arterial pressure from a cuff reading, by the traditional one-third rule and the more accurate 0.412 multiplier, against the 65 mmHg perfusion target.
MAP Calculator (Mean Arterial Pressure): with the default inputs, mean arterial pressure is 93.3.
The upper number on a cuff reading.
The lower number.
mmHg.
- MAP by the one-third rule
- 93.3
- MAP with the 0.412 multiplier
- 96.5
- Difference between the two formulas
- 3.1mmHg — grows as the pulse pressure widens.
- Pulse pressure
- 40Systolic minus diastolic, in mmHg.
- Against the 65 mmHg resuscitation target
- At or above the 65 mmHg initial target used in septic shock
Assumptions
- This is an estimate for education. It does not diagnose anything and does not replace clinical judgement.
- Pressures are in mmHg, the unit used for blood pressure in every measurement system.
- The default formula is the traditional one-third rule; the alternative is Meaney's 0.412 multiplier, fitted against directly measured pressures at cardiac catheterisation.
- Both formulas assume a typical arterial pressure waveform. They are least accurate where the pulse pressure is wide, and neither accounts for arrhythmia.
- The 65 mmHg figure is the Surviving Sepsis Campaign's initial resuscitation target for adults with septic shock on vasopressors, not a general definition of adequate blood pressure.
| Formula | Calculation | MAP (mmHg) |
|---|---|---|
| Traditional one-third rule | 80 + 40/3 | 93.3 |
| Meaney 0.412 multiplier | 80 + 0.412 × 40 | 96.5 |
The two agree closely at ordinary pulse pressures and diverge as the pulse pressure widens, because the one-third rule systematically under-reads when the pressure waveform is least sinusoidal.
How this is worked out
The formula
Traditional (one-third rule): MAP = DBP + (SBP − DBP) ÷ 3 Meaney's revision (Heart, 2000): MAP = DBP + 0.412 × (SBP − DBP) SBP = systolic pressure, DBP = diastolic pressure, both in mmHg Pulse pressure = SBP − DBP
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Systolic blood pressure
- The upper number on a cuff reading.from 0 to 300 · defaults to 120
- Diastolic blood pressure
- The lower number.from 0 to 250 · defaults to 80
- Pulse-pressure multiplier(under More options)
- Both are shown either way; this picks the headline number.0.333 — the traditional one-third rule · 0.412 — Meaney's revised multiplier (Heart, 2000)
What you get back
- Mean arterial pressuremain answer
- mmHg.
- MAP by the one-third rule
- MAP with the 0.412 multiplier
- Difference between the two formulas
- mmHg — grows as the pulse pressure widens.
- Pulse pressure
- Systolic minus diastolic, in mmHg.
- Against the 65 mmHg resuscitation target
What this assumes
- This is an estimate for education. It does not diagnose anything and does not replace clinical judgement.
- Pressures are in mmHg, the unit used for blood pressure in every measurement system.
- The default formula is the traditional one-third rule; the alternative is Meaney's 0.412 multiplier, fitted against directly measured pressures at cardiac catheterisation.
- Both formulas assume a typical arterial pressure waveform. They are least accurate where the pulse pressure is wide, and neither accounts for arrhythmia.
- The 65 mmHg figure is the Surviving Sepsis Campaign's initial resuscitation target for adults with septic shock on vasopressors, not a general definition of adequate blood pressure.
About this calculator
This is an estimate for education. It does not diagnose anything and does not replace clinical judgement.
What MAP is
Mean arterial pressure is the average pressure in the arteries across a whole cardiac cycle. It matters because it is the pressure driving blood through organs — perfusion pressure — in a way that the systolic peak is not. Systolic pressure lasts for a fraction of the cycle; diastole lasts longer. So the mean is not the midpoint of the two cuff numbers. It sits closer to the diastolic.
The rule of thumb everyone learns is that the mean lies one third of the way from diastolic up to systolic:
MAP = diastolic + (systolic − diastolic) ÷ 3
For 120/80 that gives 93 mmHg, not the arithmetic average of 100.
The multiplier is not really one third
The one-third rule is an empirical convenience, and it has a known bias. Meaney and colleagues, writing in Heart in 2000, compared cuff-derived estimates against pressures measured directly at cardiac catheterisation in 150 patients, and found that a multiplier of 0.412 matched the measured mean better than 0.333 did. Their own worked example makes the size of the problem clear: at a blood pressure of 210/90, the traditional formula gives a MAP of 130 mmHg while the 0.412 multiplier gives 139.
The error grows with pulse pressure, so it is smallest in the young and largest in exactly the patients with stiff arteries and isolated systolic hypertension where you would most want to get it right. Their data also showed the opposite effect in children, whose more compliant arteries produce a more sinusoidal waveform and a mean closer to the arithmetic average. Both multipliers are shown here.
The 65 mmHg number
The threshold most people are looking for comes from critical care. The Surviving Sepsis Campaign's 2021 international guidelines make a strong recommendation, on moderate-quality evidence, for an initial target MAP of 65 mmHg in adults with septic shock who are on vasopressors — in preference to higher targets, because trials of higher targets showed no survival benefit and more atrial fibrillation. The same guideline notes that mean pressures below roughly 60 mmHg are associated with reduced organ perfusion, which then falls roughly linearly with pressure.
Two things follow. First, 65 is a resuscitation target for a specific population, not a definition of a healthy blood pressure. Second, it applies to a measured MAP in a monitored patient, usually from an arterial line — not to a number derived from a home cuff.
Where the calculation breaks
Everything downstream of the cuff. Atrial fibrillation makes beat-to-beat pressures vary, so a single reading represents little. Very stiff arteries break the waveform assumption both formulas rest on. Cuff size, arm position and movement all shift the underlying numbers before any arithmetic happens. And many oscillometric monitors estimate the mean from the pressure oscillations themselves rather than deriving it from the systolic and diastolic numbers, so the MAP on a monitor screen may not match either formula here.
Frequently asked questions
▸What is the formula for mean arterial pressure?
The traditional rule is diastolic pressure plus one third of the pulse pressure: MAP = DBP + (SBP − DBP)/3. For 120/80 that is 93 mmHg.
▸Why is MAP not just the average of systolic and diastolic?
Because diastole lasts longer than systole, so the time-weighted average sits closer to the diastolic pressure than to the midpoint.
▸What MAP is too low?
In septic shock the Surviving Sepsis Campaign targets an initial MAP of 65 mmHg on vasopressors, and notes that means below roughly 60 mmHg are associated with reduced organ perfusion. Those are critical-care targets, not thresholds for judging a home reading.
▸Why do two formulas give different answers?
The one-third rule under-reads as the pulse pressure widens. Meaney's 2000 catheterisation study found 0.412 fitted measured pressures better; at 210/90 the two differ by 9 mmHg.
▸Why does the monitor show a different MAP?
Many oscillometric monitors estimate the mean from the amplitude of the pressure oscillations rather than deriving it from the systolic and diastolic numbers, so it may not match either formula exactly.
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