> ## Documentation Index
> Fetch the complete documentation index at: https://docs.sonohealth.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Systolic vs Diastolic: What Your Two Blood Pressure Numbers Mean

> What the top and bottom blood pressure numbers mean, why each matters, what pulse pressure tells you, and when an unusual number is worth a doctor's attention.

Every blood pressure reading has two numbers, like 120/80. Understanding what each one represents makes your home readings far more useful — and helps you know which changes matter.

<Note>
  A home monitor like the SonoHealth [BPpro](/blood-pressure/overview) is for tracking and awareness. It does not diagnose hypertension; that's a conversation to have with your doctor using consistent readings over time.
</Note>

## What is the top (systolic) number?

The **systolic** number — the top one — is the pressure in your arteries when your heart beats and pushes blood out. It's the higher of the two and tends to rise with age as arteries stiffen. In older adults, a high systolic with a normal diastolic ([isolated systolic hypertension](/blood-pressure/high-blood-pressure-when-to-worry)) is the most common pattern.

## What is the bottom (diastolic) number?

The **diastolic** number — the bottom one — is the pressure in your arteries between beats, when the heart rests and refills. A high diastolic with a normal systolic (isolated diastolic hypertension) is more common in younger adults and still deserves attention.

## What counts as normal?

For most adults, normal is **under 120/80 mmHg**. See the full [blood pressure categories](/blood-pressure/blood-pressure-chart-by-category) for elevated and high ranges. Both numbers matter — a reading is considered high if either one is elevated.

## What is pulse pressure?

**Pulse pressure** is the gap between the two numbers (systolic minus diastolic). A typical value is around 40 mmHg. A persistently wide gap can reflect stiffer arteries with age, while a very narrow gap is less common — either is worth mentioning to your doctor rather than self-interpreting.

## Which number should I worry about more?

Both are important, and their relative importance shifts with age. Rather than fixating on one number, track both over time with [good measurement technique](/blood-pressure/how-to-measure-at-home) and share consistent readings with your doctor.

<Warning>
  A reading at or above roughly 180/120 mmHg, especially with chest pain, shortness of breath, weakness, or vision changes, is a medical emergency — call 911.
</Warning>

***

**Related:** [Blood Pressure Categories](/blood-pressure/blood-pressure-chart-by-category) · [How to Measure at Home](/blood-pressure/how-to-measure-at-home) · [When High Blood Pressure Is Dangerous](/blood-pressure/high-blood-pressure-when-to-worry) · [Normal Blood Pressure by Age](/blood-pressure/normal-blood-pressure-by-age)