What do blood pressure numbers mean?
A blood pressure reading has two numbers, for example 120/80 mmHg. The top number, systolic, is the pressure in your arteries when the heart beats. The bottom number, diastolic, is the pressure between beats. High blood pressure (hypertension) usually has no symptoms but damages the heart, brain, kidneys and eyes over time — which is why it is called the “silent killer”. This free blood pressure calculator places your reading on the American Heart Association (AHA) chart.
How the calculator works
Your category is decided by whichever number is in the higher category. For example, 125/85 counts as stage 1 because the diastolic number is 80–89. The tool also calculates:
- Mean arterial pressure (MAP) = diastolic + (systolic − diastolic) ÷ 3 — the average pressure pushing blood to your organs.
- Pulse pressure = systolic − diastolic. A wide pulse pressure (over 60) in older adults can reflect stiff arteries.
Blood pressure chart for adults
| Category | Systolic (top) | Diastolic (bottom) | |
|---|---|---|---|
| Low (hypotension) | Under 90 | or | Under 60 |
| Normal | Under 120 | and | Under 80 |
| Elevated | 120 – 129 | and | Under 80 |
| High blood pressure – stage 1 | 130 – 139 | or | 80 – 89 |
| High blood pressure – stage 2 | 140 or higher | or | 90 or higher |
| Hypertensive crisis | Over 180 | and/or | Over 120 |
Some countries (including the UK) use 140/90 as the cut-off for diagnosing hypertension in a clinic. Your doctor will decide based on repeated readings.
How to measure blood pressure correctly
- Sit quietly for 5 minutes, back supported, feet flat, arm resting at heart level.
- No caffeine, smoking or exercise for 30 minutes before.
- Use the right cuff size on bare skin; don’t talk.
- Take 2–3 readings one minute apart and record the average, morning and evening for a week.
Benefits of keeping blood pressure in range
- Lower risk of stroke and heart attack — each 10 mmHg drop in systolic pressure cuts major cardiovascular events by about 20%.
- Protects your kidneys, eyes and brain.
- Diet works: the DASH eating pattern can lower systolic pressure by around 8–11 mmHg in people with hypertension.
Health warnings
- One reading is not a diagnosis — blood pressure varies through the day and with stress (“white coat” effect).
- Emergency: a reading over 180/120 with chest pain, shortness of breath, back pain, weakness, numbness, vision or speech changes needs emergency care immediately.
- Never stop or change blood pressure medicine without speaking to your doctor.
- In pregnancy, 140/90 or higher — or a sudden rise with headache or swelling — needs urgent assessment for pre-eclampsia.
Eating to lower blood pressure
Cut salt to under 5 g a day (check with the salt intake calculator), eat more potassium-rich foods (vegetables, fruit, beans, yoghurt), limit processed meats and pickles, keep a healthy waist, and stay active. Read our guides to the DASH diet and managing hypertension.
Frequently asked questions
What is a normal blood pressure?
For adults, a reading under 120/80 mmHg is normal. 120–129 systolic with diastolic under 80 is elevated, and 130/80 or higher is high blood pressure on the AHA chart.
Is 130/80 high blood pressure?
On the American Heart Association chart, 130–139 systolic or 80–89 diastolic is stage 1 high blood pressure. Some other guidelines diagnose hypertension from 140/90. Repeated readings and your doctor’s assessment decide.
Which number is more important, top or bottom?
Both matter. After about 50, the systolic (top) number becomes a stronger predictor of heart disease and stroke.
Can diet lower blood pressure?
Yes. Reducing salt, following a DASH-style diet rich in vegetables, fruit, pulses and low-fat dairy, losing excess weight and staying active can lower systolic pressure by 5–11 mmHg or more.
What is a dangerously high blood pressure?
A reading over 180/120 mmHg is a hypertensive crisis. With symptoms such as chest pain, breathlessness, weakness or vision changes, call emergency services.
Sources
- Whelton PK, et al. 2017 ACC/AHA Guideline for the Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults. Hypertension 2018;71:e13–e115.
- American Heart Association. Understanding blood pressure readings.
- Ettehad D, et al. Blood pressure lowering for prevention of cardiovascular disease and death. The Lancet 2016;387:957–967.
- Appel LJ, et al. A clinical trial of the effects of dietary patterns on blood pressure (DASH). N Engl J Med 1997.