Body · lesson 2 of 10
Blood pressure: the number that matters most
Why it leads the list, how to measure it so the number is real, and the home thresholds that should prompt action.
8 min read · reviewed October 2026
Silent, common, and fixable
High blood pressure usually causes no symptoms for years while it strains the arteries, heart, brain, kidneys and eyes. It is also one of the most treatable risks there is: lowering it prevents strokes and heart attacks in randomized trials, not just in theory.
Measuring at home catches two things a clinic visit misses:
- White-coat hypertension: high in the clinic, normal in daily life.
- Masked hypertension: normal in the clinic, high in daily life. It carries substantially increased cardiovascular risk and only shows up if you measure outside the clinic.
In a pooled analysis of 48 randomized trials and ~345,000 people, every 5 mmHg drop in systolic pressure cut the risk of major cardiovascular events by about 10%. That held whether or not people already had heart disease, and even at normal or high-normal starting pressures.
Source: Blood Pressure Lowering Treatment Trialists' Collaboration, Lancet 2021
How to take a reading that means something
- For 30 minutes before: no caffeine, exercise or smoking. Empty your bladder.
- Sit in a chair with your back supported, feet flat and legs uncrossed. Rest quietly for 5 minutes.
- Put the cuff on your bare upper arm, with the arm resting on a table so the cuff sits at heart level.
- Don't talk or look at your phone during the reading.
- Take 2 readings about 1 minute apart and record both.
- Measure in the morning (before medications and breakfast) and in the evening, for 7 days (at least 3). Average them; many protocols discard day one.
- The first time, measure both arms. From then on, use the arm that reads higher.
In a 2024 randomized crossover trial, how many mmHg did letting your arm hang unsupported at your side add to the systolic reading, compared with resting it on a desk?
Somewhere between 0 and 20 mmHg.
Reveal the answer →
+6.5 mmHg
Resting your hand in your lap added 3.9 mmHg (Liu et al., JAMA Internal Medicine 2024). Cuff size matters even more. In a 2023 trial, using a regular cuff on someone who needed a large one added about 4.8 mmHg, and on someone who needed an extra-large one it added about 19.5 mmHg (Ishigami et al., JAMA Internal Medicine 2023). That's enough to move a person into a different category. Measure around the middle of your upper arm and buy the cuff size that matches.
Reading your home average
Below 120 systolic and below 80 diastolic.
120–129 systolic, with diastolic still below 80. It's a lifestyle signal, and a reason to recheck more often.
130–139 systolic or 80–89 diastolic. In US guidelines (ACC/AHA 2017, kept in 2025), a home average of 130/80 or above counts as high blood pressure.
140 or higher systolic, or 90 or higher diastolic.
180 or higher and/or 120 or higher. See the warning below.
European guidelines (ESH 2023, ESC 2024) set home hypertension at an average of 135/85, equivalent to 140/90 in the clinic, and group the range below that differently. Ask which system your clinician uses.
The categories apply to averages, not single readings. If systolic and diastolic fall in different categories, the higher category applies.
Buy a validated upper-arm cuff
Most blood pressure monitors on sale have never had independent validation results published, and 'clinically tested' on the box doesn't guarantee they have. Check the exact model on an independent list such as the US Validated Device Listing (validatebp.org) or STRIDE BP (stridebp.org). Upper-arm cuffs are preferred. Wrist monitors are more sensitive to position, so if you use one, hold your wrist at heart level. Cuffless watches and rings are not recommended for diagnosing or managing blood pressure (2025 AHA/ACC guideline).
You rush upstairs, grab the cuff and get 146/92. What's the right next step?
- You have stage 2 hypertension, so start treating it
- Ignore it, because home readings don't count
- Sit and rest 5 minutes, measure properly, and base any conclusion on several days of averaged readings
- Keep switching arms until you get a lower number
Show the answer →
C.Sit and rest 5 minutes, measure properly, and base any conclusion on several days of averaged readings
One reading taken right after exertion mostly measures the stairs. Home readings do count (they're central to diagnosis now), but only when taken with the standard protocol and averaged over days. Re-measuring until you like the number is cherry-picking.
The Body shelf lists upper-arm and wrist monitors. Before buying, check the exact model against an independent validation list and match the cuff to your arm.