Blood pressure is one of the most important and most commonly measured health metrics — yet many people do not fully understand what their numbers mean. This guide explains everything you need to know about blood pressure, from how to read your results to what to do if they are high.
What blood pressure numbers mean
Blood pressure is recorded as two numbers, written as one over the other — for example, 120/80 mmHg. These numbers measure the pressure in your arteries in millimetres of mercury (mmHg).
The top number (systolic pressure) is the pressure when your heart contracts and pumps blood out into the arteries. The bottom number (diastolic pressure) is the pressure when your heart relaxes between beats.
Both numbers matter, and both are used to categorise blood pressure.
Blood pressure categories
Blood pressure categories used by most health organisations:
- Normal: Below 120/80 mmHg
- Elevated: 120–129 systolic and less than 80 diastolic
- Stage 1 hypertension: 130–139/80–89 mmHg
- Stage 2 hypertension: 140/90 mmHg or higher
- Hypertensive crisis: Above 180/120 mmHg — requires immediate medical attention
Low blood pressure (hypotension) is generally defined as below 90/60 mmHg, though what is "too low" depends on individual symptoms.
Why blood pressure matters
High blood pressure (hypertension) is often called the "silent killer" because it typically causes no symptoms while silently damaging blood vessels and organs over years. Consistently elevated blood pressure is the leading modifiable risk factor for:
- Heart attack
- Stroke — the relationship between blood pressure and stroke risk is the strongest in medicine
- Heart failure
- Kidney disease
- Peripheral artery disease
- Aortic aneurysm
- Vascular dementia
Reducing systolic blood pressure by just 10 mmHg reduces stroke risk by approximately 35% and heart attack risk by approximately 20% — across all baseline levels.
How to measure blood pressure accurately
Blood pressure varies continuously throughout the day in response to activity, stress, temperature, and time of day. A single reading in a clinical setting may not represent your true average blood pressure.
For accurate home monitoring:
- Rest quietly for five minutes before measuring
- Sit with back supported, feet flat on floor, arm at heart level
- Do not smoke, exercise, or consume caffeine in the 30 minutes before measurement
- Take two readings, one minute apart, morning and evening for seven days
- Record all readings and share with your doctor
- Use a validated upper-arm cuff monitor (wrist monitors are less accurate)
White coat hypertension and masked hypertension
White coat hypertension — blood pressure that is elevated in clinical settings but normal at home — affects up to 15% of people diagnosed with hypertension. Masked hypertension is the opposite: normal readings in clinic but elevated at home. Home monitoring and ambulatory blood pressure monitoring (worn for 24 hours) are important diagnostic tools for these reasons.
Lifestyle changes that lower blood pressure
For those with elevated or stage 1 hypertension, lifestyle changes can often normalise blood pressure without medication. For those on medication, they reduce the number or dose of drugs needed.
Reduce salt intake — this is the single most effective dietary intervention. Reducing from the UK average of 8g to under 6g daily can reduce systolic pressure by 4–8 mmHg. Check food labels — bread, processed meats, and ready meals are major hidden sources.
Follow the DASH diet — rich in fruits, vegetables, wholegrains, and low-fat dairy. Proven to reduce systolic pressure by 8–14 mmHg.
Exercise regularly — 150 minutes of moderate aerobic exercise per week reduces systolic pressure by 4–9 mmHg.
Maintain healthy weight — each kilogram of weight lost reduces systolic pressure by approximately 1 mmHg.
Limit alcohol — consistently heavy drinking raises blood pressure significantly. The relationship is dose-dependent.
Stop smoking — each cigarette temporarily raises blood pressure. Chronic smoking causes arterial stiffening.
Manage stress — chronic psychological stress activates the sympathetic nervous system, raising blood pressure over time.
Blood pressure medications
When lifestyle changes alone are insufficient, medications are effective and well-tolerated. First-line options include ACE inhibitors, angiotensin receptor blockers (ARBs), calcium channel blockers, and thiazide diuretics. Many people require two or more medications in combination to reach their target.
If your GP prescribes blood pressure medication, it is important to take it consistently — missing doses allows blood pressure to rise. Most medications need several weeks to reach their full effect. Side effects are common initially but often improve, and alternatives are available if needed.
How often to have your blood pressure checked
Adults aged 40 and over should have blood pressure checked at least every five years. Those with elevated or borderline readings should be checked annually. People on medication or with conditions linked to hypertension (diabetes, kidney disease) should be monitored more frequently, as advised by their GP.
Editorial note: This article was written by the SymptomSense editorial team in accordance with our editorial policy. It is reviewed against NHS, WHO, and Mayo Clinic guidelines and updated regularly. Last reviewed June 2026. This article is for informational purposes only and does not constitute medical advice.