BP LogBlood pressure variability calculator
Paste or type your readings to see how much they vary: standard deviation, coefficient of variation and average real variability, for the top and bottom numbers.
Measure how much your readings vary
Paste or type readings in the order you took them, one per line, like 128/82. Several readings on one line, separated by spaces or commas, work too.
0 readings found
| Mean | SD | CV | ARV | Range | |
|---|---|---|---|---|---|
| Top (systolic) | · | · | · | · | · |
| Bottom (diastolic) | · | · | · | · | · |
Add at least 3 readings. Variability means more with 12 or more, such as a week of morning and evening readings.
What the numbers mean
- Mean: the average of the readings.
- SD (standard deviation): how far readings typically sit from the mean, in mmHg.
- CV (coefficient of variation): the SD as a percentage of the mean, so people with higher and lower averages can be compared.
- ARV (average real variability): the average absolute change between one reading and the next.
Research links higher reading-to-reading variability with higher cardiovascular risk, but it is not used to set a blood pressure category, and there is no target value for it. Our guide on why blood pressure is different every time covers the everyday reasons readings move.
How it is calculated
The top numbers and the bottom numbers are treated as two separate series, in the order entered. SD is the sample standard deviation (dividing by the number of readings minus one). CV is SD divided by the mean, times 100. ARV is the sum of the absolute differences between consecutive readings, divided by the number of readings minus one. The calculation comes from the shared code library behind the BP Log apps.
Common questions
Is it normal for blood pressure to vary?
Yes. Blood pressure changes with breathing, posture, activity, stress, caffeine, sleep and the time of day. Two readings a minute apart often differ by several points, which is one reason guidelines average them.
What is a normal amount of variability?
There is no agreed normal value for home readings, and the 2025 ACC/AHA guideline does not set one. These numbers are most useful for comparing your own readings over time, measured the same way.
What is the difference between SD and ARV?
Standard deviation (SD) measures how spread out the readings are around their average, regardless of order. Average real variability (ARV) is the average jump from one reading to the next, so it depends on the order you enter them.
How many readings do I need?
At least 3 to get a number, but 12 or more, such as a week of morning and evening readings, gives a much steadier estimate.
- Parati G, et al. Blood pressure variability: methodological aspects, clinical relevance and practical indications for management. A European Society of Hypertension position paper (Journal of Hypertension, 2023): Standard deviation, coefficient of variation and average real variability as measures of reading-to-reading variability; no agreed normal values for home readings
- Muntner P, et al. Measurement of Blood Pressure in Humans: A Scientific Statement From the American Heart Association (Hypertension, 2019): How to measure; home protocol of 2 readings a minute apart, morning and evening, for 7 days; cuff sizes by arm circumference; white coat and masked hypertension definitions; home 130/80 corresponds to office 130/80
The free iPhone app times two readings a minute apart, averages them, keeps your morning and evening numbers apart, and builds a report for your doctor.
Other ways to track: desktop, Excel and printable logs