The two numbers
MedlinePlus describes blood pressure as the force of your blood pushing against the walls of your arteries, measured in millimetres of mercury, mm Hg. A reading has two parts. The systolic pressure, the first and higher number, is the pressure when the heart beats and pushes blood out. The diastolic pressure, the second and lower number, is the pressure between beats, when the heart rests. A reading of 118/76 means a systolic pressure of 118 and a diastolic of 76. The pressure converter turns mm Hg into kilopascals for anyone reading a European device.
The categories
| Category | Systolic (top number) | Diastolic (bottom number) | |
|---|---|---|---|
| Normal | less than 120 | and | less than 80 |
| Elevated | 120 to 129 | and | less than 80 |
| High blood pressure, stage 1 | 130 to 139 | or | 80 to 89 |
| High blood pressure, stage 2 | 140 or higher | or | 90 or higher |
| Hypertensive crisis (seek medical care right away) | higher than 180 | and/or | higher than 120 |
The middle column matters. For a reading to be normal, both numbers have to be under their lines: less than 120 and less than 80. For the high categories a single number is enough: 130 to 139 or 80 to 89 is stage 1. The CDC publishes the same thresholds with the two high stages combined into one hypertension category beginning at 130 or higher or 80 or higher. The crisis row is the one MedlinePlus labels dangerously high blood pressure, with the instruction to seek medical care right away.
Ten readings, sorted
Applying the cut points to example readings shows how the worse number decides. Each row is one reading; the category is the one its higher-ranking number falls into.
| Reading (mm Hg) | Systolic category | Diastolic category | Category |
|---|---|---|---|
| 112/72 | Normal | Normal | Normal |
| 118/79 | Normal | Normal | Normal |
| 124/76 | Elevated | Normal | Elevated |
| 128/84 | Elevated | High blood pressure, stage 1 | High blood pressure, stage 1 |
| 136/78 | High blood pressure, stage 1 | Normal | High blood pressure, stage 1 |
| 139/89 | High blood pressure, stage 1 | High blood pressure, stage 1 | High blood pressure, stage 1 |
| 142/86 | High blood pressure, stage 2 | High blood pressure, stage 1 | High blood pressure, stage 2 |
| 150/96 | High blood pressure, stage 2 | High blood pressure, stage 2 | High blood pressure, stage 2 |
| 176/118 | High blood pressure, stage 2 | High blood pressure, stage 2 | High blood pressure, stage 2 |
| 184/110 | Hypertensive crisis | High blood pressure, stage 2 | Hypertensive crisis |
Two rows show the asymmetry. 136/78 is stage 1 on the systolic number although the diastolic is normal; 128/84 is stage 1 on the diastolic number although the systolic is only elevated. And 184/110 is a crisis on the systolic alone, because the crisis row reads "and/or".
Reading your own numbers
- One reading is not a category. Pressure moves with activity, caffeine, stress and the time of day; a category is for a pattern of readings, taken rested and seated, which is why doctors ask for several.
- Check the device and the cuff. A cuff that is too small reads high; an arm held below heart level reads high.
- Record both numbers and the time. The category depends on each, and the trend is more useful to a clinician than any single pair.
- Above 180 or above 120, act. Rest a few minutes and recheck; if it stays there, or you have symptoms, seek medical care right away, as the crisis row says.
Blood pressure sits next to the other numbers a check-up produces. The BMI calculator and the heart rate zones page cover two of the others; none of them replaces a conversation with a doctor, and this guide reports the published categories only, not what any reading means for a particular person.
Frequently asked questions
What is a normal blood pressure?
A systolic reading of less than 120 and a diastolic reading of less than 80, written 120/80 and measured in millimetres of mercury. That is the "normal" category on the scale MedlinePlus and the CDC publish; both numbers have to be under the line, and a reading of 120 to 129 over less than 80 is already the next category, elevated.
What do the two numbers mean?
The first, systolic, is the pressure in the arteries when the heart beats; the second, diastolic, is the pressure between beats when the heart rests. MedlinePlus describes blood pressure itself as the force of blood pushing against the walls of the arteries. A reading is always both numbers, and a category is assigned by whichever number falls in the higher category.
Is 130 over 80 high blood pressure?
Yes, by the categories MedlinePlus lists: a systolic reading of 130 to 139 or a diastolic reading of 80 to 89 is high blood pressure, stage 1. The CDC draws the same line, calling 130 or higher, or 80 or higher, hypertension. Stage 2 begins at 140 or higher, or 90 or higher.
When is blood pressure an emergency?
MedlinePlus lists a hypertensive crisis as a reading higher than 180 and/or higher than 120 and labels it dangerously high blood pressure for which you should seek medical care right away. A single high reading at home can be rechecked after a few minutes of rest, but a reading in that range, especially with symptoms, is a reason to get help, not to wait.
Why do the categories use "or" for high blood pressure but "and" for normal?
Because a reading is classified by its worse number. To be normal, both numbers must be low. To be stage 1, it is enough for either the systolic to be 130 to 139 or the diastolic to be 80 to 89. A reading of 118 over 85 is therefore stage 1 on the diastolic number alone, even though the systolic is normal.
Sources
- MedlinePlus, US National Library of Medicine: High blood pressure (blood pressure as the force of blood against artery walls; systolic and diastolic; the categories normal, elevated, stage 1, stage 2 and hypertensive crisis with their cut points)
- CDC: About high blood pressure (normal below 120 and below 80; elevated 120 to 129 and below 80; hypertension 130 or higher or 80 or higher; systolic and diastolic defined; mm Hg)