Understanding your blood pressure readings: what the numbers actually mean

What the two numbers mean

Every blood pressure reading has two numbers, measured in millimeters of mercury (mmHg). The top number — systolic pressure — measures the force when your heart contracts. The bottom number — diastolic pressure — measures the force when your heart rests between beats.

A reading of 120/80, for example, means a systolic pressure of 120 and a diastolic pressure of 80.

What counts as normal

For most adults, widely used clinical thresholds look like this:

• Normal: below 120/80
• Elevated: systolic 120–129 with diastolic below 80
• High (stage 1): systolic 130–139 or diastolic 80–89
• High (stage 2): systolic 140 or higher, or diastolic 90 or higher

These are screening thresholds, not a diagnosis. A single high reading — especially during stress, illness, or after caffeine — does not mean you have hypertension.

How to get an accurate home reading

Home readings are most useful when they are consistent. Sit with your back supported, feet flat, and arm at heart level. Rest quietly for five minutes first, avoid caffeine and exercise for at least 30 minutes beforehand, and take two readings a minute apart.

Track your readings over days or weeks rather than reacting to one number. Patterns matter far more than isolated values.

When to talk to a clinician

Seek prompt professional advice if you repeatedly record readings at or above 130/80, if a single reading exceeds 180/120, or if high readings come with chest pain, shortness of breath, or neurological symptoms — in which case use emergency services.

Bring your log to the appointment. A week of morning and evening readings tells a clinician far more than one office measurement.

This article is educational and does not diagnose, treat, or replace professional medical advice.