Blood Pressure Calculator
Enter a blood pressure reading to see its NHS/NICE-aligned category, pulse pressure and mean arterial pressure (MAP).
NHS/NICE-Aligned Category Ranges
Blood Pressure Calculator
Our Blood Pressure Calculator helps you understand what a blood pressure reading means by categorising it against NHS and NICE-aligned thresholds, and calculates two related figures — pulse pressure and mean arterial pressure (MAP) — that your GP may also refer to. It is a general information tool, not a diagnostic one; a single reading is never enough to diagnose high or low blood pressure.
Understanding Your Blood Pressure Reading
A blood pressure reading has two numbers, written as systolic over diastolic (for example, “120 over 80”, or 120/80 mmHg):
- Systolic pressure (the top, higher number) is the pressure in your arteries when your heart beats and pushes blood out.
- Diastolic pressure (the bottom, lower number) is the pressure in your arteries when your heart rests between beats.
Both numbers are measured in millimetres of mercury (mmHg). If either number falls into a higher category than the other, your overall reading is generally classed using the higher of the two — this calculator follows that same convention.
NHS/NICE-Aligned Blood Pressure Categories
The UK uses NHS and NICE (guideline NG136) thresholds for diagnosing high blood pressure, which differ slightly depending on whether a reading was taken in a clinic/GP setting or measured at home. Home and ambulatory (24-hour) readings use a threshold roughly 5 mmHg lower than clinic readings, because people often measure slightly lower blood pressure at home than in a clinical setting (“white coat” effect). The table below shows the clinic thresholds; use the calculator above with the “Home / Self-Monitor” setting selected for home-adjusted ranges.
| Category | Clinic/GP Reading |
|---|---|
| Low blood pressure | Below 90/60 mmHg |
| Not high blood pressure | 90/60 up to below 140/90 mmHg |
| High blood pressure | 140/90 mmHg or higher |
Source: NHS and NICE guideline NG136; British Heart Foundation. These are general population thresholds — your GP may set a different personal target based on your health history. A reading with a systolic of 180 mmHg or higher or a diastolic of 120 mmHg or higher may indicate severe hypertension and needs urgent attention — see the guidance below.
What Are Pulse Pressure and Mean Arterial Pressure (MAP)?
Pulse pressure is simply the systolic reading minus the diastolic reading. For a reading of 120/80 mmHg, the pulse pressure is 40 mmHg. A very narrow or very wide pulse pressure can sometimes be clinically relevant, but it’s normally interpreted by a healthcare professional alongside the rest of your reading, not in isolation.
Mean arterial pressure (MAP) is the average pressure in your arteries across a full heartbeat cycle. Because your heart spends more time in the resting (diastolic) phase than the pumping (systolic) phase, MAP isn’t a simple average of the two numbers — it’s calculated as diastolic pressure plus one third of the pulse pressure: MAP = DBP + ⅓(SBP − DBP). A MAP of roughly 70–100 mmHg is generally considered adequate to perfuse the body’s major organs, though this is a general clinical reference range rather than a target for the general public to aim for. MAP is a supplementary figure only — this calculator, and clinical practice generally, uses your systolic and diastolic numbers to classify your blood pressure category, not MAP.
What Should I Do With My Result?
- Not high blood pressure: No immediate action needed, but it’s worth having your blood pressure checked periodically as part of routine health checks.
- High blood pressure (above normal): Book an appointment with your GP or pharmacist. They’ll usually want several readings over time, sometimes using home or 24-hour monitoring, before making a diagnosis or discussing treatment.
- Systolic 180 mmHg or higher, or diastolic 120 mmHg or higher: This calculator will flag this as a reading that may need urgent attention. If you have life-threatening symptoms such as chest pain, severe breathlessness, sudden weakness, vision loss, or confusion, call 999 immediately. Without those symptoms, rest for a few minutes, take a second reading, and if it stays this high, seek urgent guidance from NHS 111 or your GP practice the same day.
- Low blood pressure: Only usually a concern if it comes with symptoms such as dizziness, fainting or fatigue. If you have symptoms, speak to your GP.
Getting an Accurate Reading
Blood pressure readings can vary considerably based on measurement technique. For the most accurate result:
- Sit quietly for at least five minutes beforehand, with your back supported and feet flat on the floor.
- Support your arm at roughly heart height, and keep it still during measurement.
- Avoid caffeine, exercise and smoking for at least 30 minutes before measuring.
- Take two or three readings a minute or two apart and use the average, rather than relying on a single reading.
- Use a properly fitted cuff — a cuff that’s too small can produce an artificially high reading.
Frequently Asked Questions
What is a healthy blood pressure reading?
Under the NHS/NICE-aligned thresholds this calculator uses, any clinic/GP reading below 140/90 mmHg (or below 135/85 mmHg for a home reading) is classed as “not high.” Many sources also describe roughly 90/60 to 120/80 mmHg specifically as an “ideal” reference point within that range. This is a general population guide; your GP may discuss a different personal target with you based on your individual health history.
What’s the difference between systolic and diastolic blood pressure?
Systolic pressure (the top number) is the pressure in your arteries when your heart beats and pushes blood out. Diastolic pressure (the bottom number) is the pressure when your heart rests between beats. Both numbers matter, and either one being elevated can push your overall reading into a higher category.
What is pulse pressure?
Pulse pressure is your systolic reading minus your diastolic reading. For example, a reading of 120/80 mmHg has a pulse pressure of 40 mmHg. It’s a supplementary figure that clinicians sometimes consider alongside your main reading, not a standalone diagnostic measure.
What is mean arterial pressure (MAP)?
Mean arterial pressure is the average pressure in your arteries across a full heartbeat, calculated as diastolic pressure plus one third of the pulse pressure (MAP = DBP + ⅓(SBP − DBP)). A MAP of roughly 70 to 100 mmHg is generally considered adequate to perfuse the body’s major organs, though this is a clinical reference range rather than a personal target. MAP is a supplementary figure only — it is not used to classify your blood pressure category, which is based on your systolic and diastolic numbers.
What should I do if my reading is 180/120 or higher?
A reading with a systolic of 180 mmHg or higher or a diastolic of 120 mmHg or higher may indicate severe hypertension. This calculator will flag a reading in this range. If you have life-threatening symptoms such as chest pain, severe breathlessness, sudden weakness, vision loss, or confusion, call 999 immediately. If you don’t have these symptoms, rest for a few minutes and take a second reading; if it remains this high, seek urgent guidance from NHS 111 or your GP practice the same day.
Does this calculator diagnose high blood pressure?
No. It categorises a single reading against NHS/NICE-aligned thresholds for general information only. GPs diagnose hypertension based on a consistent pattern across multiple readings over time, sometimes using 24-hour or home monitoring, not a single measurement. If your reading falls outside the normal range, speak to your GP or pharmacist.
Why do home and clinic blood pressure thresholds differ?
Many people measure slightly lower blood pressure at home than in a clinical setting, an effect sometimes called “white coat hypertension.” To account for this, NICE guideline NG136 sets the home and 24-hour ambulatory monitoring threshold for high blood pressure about 5 mmHg lower than the equivalent clinic threshold (135/85 mmHg at home versus 140/90 mmHg in clinic). A home reading of 135/85 mmHg or higher is above the usual home-monitoring threshold for high blood pressure. A diagnosis normally requires repeated readings and appropriate clinical assessment.
Can one high reading mean I have hypertension?
Not on its own. Blood pressure naturally fluctuates throughout the day and can be temporarily raised by stress, caffeine, exercise, or simply being in a clinical setting. GPs typically want to see a consistent pattern across multiple readings, often including home or 24-hour monitoring, before diagnosing hypertension.