Mean arterial pressure (MAP): how to calculate it from a blood pressure reading
Mean arterial pressure (MAP) is an estimate of the average pressure in the arteries over one heartbeat. From a cuff reading, MAP = diastolic + (systolic − diastolic) ÷ 3. For 120/80 mm Hg, that's 80 + 40 ÷ 3 = 93.3 mm Hg.
Not a medical device. Not a diagnosis or dosing recommendation.
What is mean arterial pressure?
A blood pressure reading has two numbers: systolic (the peak, when the heart contracts) and diastolic (the low point, between beats). The heart spends more of each beat relaxing than contracting, so the average sits closer to the diastolic number than to the midpoint. The usual estimate adds one third of the gap between the two numbers to the diastolic pressure.
On this page, MAP means mean arterial pressure, a blood pressure measure. It doesn't mean a map or any other use of the letters.
Magent's calculator uses the conventional estimate from a cuff systolic and diastolic pressure. It cites Sesso and colleagues, who compared systolic, diastolic, pulse and mean arterial pressure in Hypertension in 2000. It isn't the mean measured with an arterial line.
This page explains the arithmetic. It doesn't give a target, and it doesn't say what a value means for a particular person.
The MAP formula
MAP = diastolic + (systolic − diastolic) ÷ 3Exact expression the calculator uses:
MAP_mm_hg = diastolic_mm_hg + (systolic_mm_hg - diastolic_mm_hg) / 3In words: subtract diastolic from systolic to get the pulse pressure, divide it by 3, and add the result to the diastolic pressure. Magent's calculator reports MAP to 1 decimal place.
The same formula can be written as one third of systolic plus two thirds of diastolic. Both give the same answer.
What each part means
| Term | Plain-English meaning | Unit | Accepted range |
|---|---|---|---|
systolic_mm_hg | Systolic pressure from a cuff, the top number | mm Hg | 50–250 |
diastolic_mm_hg | Diastolic pressure from a cuff, the bottom number | mm Hg | 20–160, and below systolic |
pulse_pressure_mm_hg | Systolic minus diastolic | mm Hg | Returned |
map_mm_hg | Mean arterial pressure | mm Hg | 1 decimal place |
How the formula works
- Pulse pressure: systolic − diastolic.
- One third of it: pulse pressure ÷ 3.
- Add to diastolic.
- Round to 1 decimal place.
The calculator rejects a diastolic pressure that's equal to or higher than the systolic.
Worked examples
These use Magent's own expected values for the calculator.
Example 1: 120/80 mm Hg
- Pulse pressure: 120 − 80 = 40
- 40 ÷ 3 = 13.333…
- MAP: 80 + 13.333…, rounded to 93.3 mm Hg
The other way: (120 + 2 × 80) ÷ 3, rounded to the same 93.3 mm Hg.
Example 2: 160/70 mm Hg
- Pulse pressure: 160 − 70 = 90
- 90 ÷ 3 = 30
- MAP: 70 + 30 = 100.0 mm Hg
Example 3: 110/90 mm Hg
- Pulse pressure: 110 − 90 = 20
- 20 ÷ 3 = 6.666…
- MAP: 90 + 6.666…, rounded to 96.7 mm Hg
Example 4: 100/85 mm Hg
- Pulse pressure: 100 − 85 = 15
- 15 ÷ 3 = 5
- MAP: 85 + 5 = 90.0 mm Hg
Examples 2 and 3 have similar MAP values but very different pulse pressures. MAP alone doesn't show how wide the gap is, which is why the calculator returns the pulse pressure too.
History of the formula
Magent's calculator cites Sesso HD, Stampfer MJ, Rosner B and colleagues, Systolic and diastolic blood pressure, pulse pressure, and mean arterial pressure as predictors of cardiovascular disease risk in men, Hypertension, 2000 (volume 36, issue 5, pages 801–807). The abstract describes following male physicians prospectively and comparing systolic, diastolic, pulse and mean arterial pressure as predictors of cardiovascular disease.
The abstract doesn't give a formula. Magent's calculator uses the conventional estimate: diastolic plus one third of the pulse pressure, the same as one third of systolic plus two thirds of diastolic.
When it's used
MAP can be worked out from any cuff reading that has a systolic and a diastolic pressure.
Where it's used
Anywhere a cuff blood pressure is taken. The formula needs the two cuff numbers and nothing else.
Who uses it
Anyone with a systolic and diastolic reading can do the arithmetic.
Limits of the calculation
- It's the conventional one-third estimate from cuff pressures, not the mean measured through an arterial line.
- It doesn't apply arterial-line averaging or form-factor corrections.
- It doesn't apply blood pressure thresholds or targets.
- The result depends on the cuff numbers entered.
- This page doesn't say what a value means for a particular person.
Clinical decisions belong to a qualified clinician who knows the patient.
How it differs from related measures
Glossary
- Systolic pressure: the highest pressure in the arteries, when the heart contracts.
- Diastolic pressure: the lowest pressure, between heartbeats.
- Pulse pressure: systolic minus diastolic.
- mm Hg: millimetres of mercury, the unit for blood pressure.
- Arterial line: a thin tube in an artery that measures pressure continuously.
Common mistakes
- Taking the midpoint. (Systolic + diastolic) ÷ 2 overestimates MAP; the formula weights diastolic more.
- Dividing the whole systolic by 3. Divide the pulse pressure by 3, then add diastolic.
- Swapping the numbers. Diastolic has to be below systolic.
- Reading MAP as a target. The calculator returns a number, not a goal.
- Confusing the letters. MAP here is mean arterial pressure.
Source
Sesso HD, Stampfer MJ, Rosner B, et al. Systolic and diastolic blood pressure, pulse pressure, and mean arterial pressure as predictors of cardiovascular disease risk in men. Hypertension. 2000;36(5):801-807. DOI: 10.1161/01.HYP.36.5.801. PMID: 11082146
Frequently asked questions
How do you calculate MAP from blood pressure?
Subtract diastolic from systolic, divide by 3, and add the diastolic pressure. For 120/80 mm Hg, 80 + 40 ÷ 3 = 93.3 mm Hg.
What is the MAP for 120/80?
93.3 mm Hg, to 1 decimal place.
Why isn't MAP halfway between systolic and diastolic?
The heart spends more of each beat relaxing than contracting, so the average pressure sits closer to the diastolic number.
Is a calculated MAP the same as an arterial-line MAP?
No. The calculator estimates MAP from two cuff numbers. An arterial line measures it.
Does MAP mean something else here?
No. On this page, MAP is mean arterial pressure.