Blood Pressure Calculator
A clear, practical calculator with instant results and an explained formula.
Blood Pressure Calculator
How to use this calculator
Enter the values and calculate. Adjust inputs to compare results.
(systolic + 2 × diastolic) ÷ 3; educational estimate only.
Informational estimate only. Verify important financial, health, engineering, or regulatory decisions with a qualified professional.
Understanding the result
This tool estimates mean arterial pressure (MAP), the average pressure driving blood through the arteries during one cardiac cycle. It uses systolic and diastolic readings in millimetres of mercury. MAP is not the same as a blood-pressure category, and this result cannot diagnose high or low blood pressure.
What the calculation is doing
The formula is diastolic pressure plus one third of pulse pressure: DBP + (SBP − DBP) ÷ 3. This is algebraically the same as (SBP + 2 × DBP) ÷ 3. It gives diastole twice the weight because, at a normal resting heart rate, the heart generally spends longer in diastole than systole.
A worked reading
For 120/80 mmHg, pulse pressure is 40. One third of 40 is about 13.3, so estimated MAP is 93.3 mmHg. The calculator reports that estimate; it does not label the 120/80 reading or replace interpretation of the original two numbers.
Before relying on the number
- Use a validated cuff of the correct size and follow its instructions.
- Rest quietly and repeat readings when accuracy matters; a single measurement can be unrepresentative.
- The approximation is less reliable when the heart rate or rhythm is unusual.
- Urgent symptoms or extremely abnormal readings need medical attention, not an online calculation.
Record the original systolic and diastolic values alongside the estimate. Clinicians make decisions from the full measurement, symptoms, repeated readings and medical context—not MAP alone.
When comparing readings, keep conditions similar: same arm, posture, cuff and rest period. Note the time and any factors such as exercise, caffeine or missed medicine that may affect interpretation. The calculator cannot correct a poor measurement, so improving the input is more valuable than calculating additional decimal places.
Practical questions about Blood Pressure Calculator
Does this calculator diagnose hypertension?
No. It estimates MAP and does not classify or diagnose blood pressure.
Why is diastolic pressure counted twice?
The common resting approximation reflects the longer portion of the cardiac cycle usually spent in diastole.
Can I enter readings from a smartwatch?
Use measurements from a device validated for blood-pressure measurement and follow its directions.
Should I average several results?
Repeated correctly taken readings often provide more context, but follow a clinician’s instructions for monitoring.
Health note: This page provides a general educational estimate. It is not medical advice, diagnosis, monitoring guidance or emergency care.