How accurate are blood pressure monitors?

Anyone looking to buy a blood pressure monitor can feel overwhelmed by the choices. There are countless manufacturers and many offer several models. You can find cheap bargains from around 10, but you can also spend triple-digit amounts.

That naturally raises the question of whether a cheap device measures just as well as an expensive one. To make a short answer: you can't say that directly. We need to explain a bit.

Approval as a medical device

Monitors are medical devices and there is a specific approval process for them. This involves regulations, standards and laws. The measurement accuracy is also checked as part of this approval.

Technical testing

This includes technical testing, for example checking the pressure gauge and the cuff. But that tells you little about how accurate the measurements are on a person.

Clinical validation

That's why a device needs clinical validation. Simply put, they measure the blood pressure of a certain number of people. Those measurements are compared to a measurement after Korotkoff, i.e. using a stethoscope. A test protocol defines how closely the values must match for the device to be approved. The protocol also specifies the number of patients and which ones are included in the test.

Test protocols

There isn't just one test protocol. They can differ quite a bit. The better-known ones are the protocols from ESH, BHS, AAMI and DHL. However, manufacturers weren't required to follow them.
With the Medical Device Regulation - the new medical device law from 2017 - there is now a standard ISO 81060 (AAMI/ESH/ISO) that represents a mandatory protocol. However, many devices on the market still have old approvals.

Comparison table of validation protocols:

	ESH	BHS	AAMI	DHL	AAMI/ESH/ISO
Number of participants	33	85	>=85	96	>=85
Age	>=25	15-80	>12	>20	>12
Blood pressure ranges (SBP = systolic blood pressure, DBP = diastolic blood pressure)	SBP (mmHg): <130: 10-12 participants, 130-160: 10-12, >160 mmHg: 10-12 DBP (mmHg): <80: 10-12, 80-100: 10-12, >100: 10-12	SBP (mmHg): <90: ≥8 participants, 90-129: ≥20, 130-160: ≥20, 161-180: ≥20, >180: ≥8, DBP (mmHg): <60: ≥8 participants, 60-79: ≥20, 80-100: ≥20, 101-110: ≥20, >110: ≥8	SBP (mmHg): ≤100 mmHg: ≥5% of measurements, ≥140 mmHg: ≥20%, ≥160: ≥5%, DBP (mmHg): ≤60 mmHg: ≥5%, ≥85 mmHg: ≥20%, ≥100 mmHg: ≥5%	20-40 years SBP (mmHg): ≤140: 12 participants ≥141: 12 DBP (mmHg): ≤90: 12 ≥91: 12 41-70 years: SBP: ≤120: 8 121-140: 16 141-160: 16 ≥161: 8 DBP: ≤80: 8 81-90: 16 91-100: 16 ≥101: 8 ≥71 years: SBP: ≤140: 12 >141: 12 DBP: ≤90: 12 >91: 12	SBP (mmHg): ≤100 mmHg: ≥5% of measurements ≥140 mmHg: ≥20%, ≥160: ≥5%, DBP (mmHg): ≤60 mmHg: ≥5%, ≥85 mmHg: ≥20%, ≥100 mmHg: ≥5%
Approval criteria	Criteria based on the number of measurements with a difference between the test device and the reference blood pressure of 5, 10, 15 mmHg. There are criteria for individual blood pressure measurements (Part 1) and for individual participants (Part 2). Part 1: Passes if 73.7% (73/99) of the differences are 5 mmHg, 87.9% (87/99) are 10 mmHg, and 97.6% (96/99) are 15 mmHg. Part 2 (accuracy): Number of participants with 0, 2 or 3 absolute differences 5 mmHg.	A grading system (A, B, C, D) based on the counts of paired differences within 5, 10, 15 mmHg, calculated separately for each observer and separately for SBP and DBP. Additionally, mean differences 5 mmHg and standard deviation 8 mmHg are recommended (AAMI recommendations).	Criteria are based on mean blood pressure differences and their standard deviations, applied to individual measurements and to individual participants. Criteria 1 and 2 should be applied to both SBP and DBP. Criterion 1 (for individual measurements): the mean blood pressure difference is 5 mmHg and the standard deviation is 8 mmHg. Criterion 2 (for individual participants): the mean difference and the standard deviation of a participant's measurements must fall within the threshold defined by the mean from Criterion 1.	Criteria based on mean differences, standard deviation, and a points system for paired SBP and DBP measurements. A device passes if it meets all of the following: mean difference for SBP and DBP 5 mmHg, standard deviation 8 mmHg, and a score 55% of the maximum possible points.	Criteria based on the mean blood pressure differences (test vs. reference) and their standard deviations for individual measurements and for individual participants. Criteria 1 and 2 should be applied to both SBP and DBP. Criterion 1 (for individual measurements): the mean blood pressure difference is 5 mmHg and the standard deviation is 8 mmHg. Criterion 2 (for individual participants): the mean difference and the standard deviation of the averaged blood pressure differences must lie within a threshold defined by the mean from Criterion 1. In addition, the counts of absolute differences within 5, 10 and 15 mmHg (ESH-IP2) and standardized BlandAltman scatter plots are submitted. The mean testreference blood pressure difference and the standard deviation per cuff subgroup must be reported for the test device without pass/fail criteria.

There are many other criteria as well, such as the selection of participants and how the measurements are taken. Even so, you can see that the tests can differ significantly.

Accuracy

So you can't just state how accurate a device is. But you can say whether it has passed a validation a test. The more demanding the protocol, the better. You can also view some test protocols online.

Why clinically validate?

Der Arzt misst mit der Methode nach Korotkoff

But why is this validation needed at all? It's because today's devices work oscillometrically. They don't actually measure systolic and diastolic blood pressure the way the Korotkoff method with a stethoscope does. Instead, the two values are derived from the maximal arterial oscillation using algorithms. This can cause problems, especially in people with arrhythmia, increased arterial stiffness, diabetes or tremor. Clinical validation is used to ensure that these derivations work well for as many people as possible.

What does this mean?

Devices are tested for accuracy before they can be sold. But let's be honest: the range of what is still approved is quite wide.
There isn't one perfect device for everyone. You should choose one that shows the most reliable results in a test group similar to you (age, sex, arm circumference, heart rhythm disorders, arterial stiffness, etc.). And that's the tricky part, where it unfortunately becomes something of a science.

Because single measurements can be inaccurate, don't be alarmed by a single reading. More important and much more reliable are regular measurements that allow you to look at all values over time. For that, for example, BloodPressureDB is useful to mainly see changes over time and act appropriately.

Download the app now and benefit from the clear layout.

This article comes from BloodPressureDB – the leading app since 2011 that helps hundreds of thousands monitor their blood pressure every day. Our content is based on carefully researched, evidence-based data and is continuously updated (as of 11/2025).

Author Horst Klier has been intensively involved with high blood pressure since 2002 initially from personal experience and, since 2009, as the developer of BloodPressureDB. Thanks to his app and specialist platform used by millions as well as numerous publications, he is now regarded as a recognised blood pressure expert. As the author of several health guides and professional articles, he makes complex information understandable and practical.

We hope you found the article helpful. Accurate measurements are essential for good blood pressure control. Our app BloodPressureDB can help with that. Clear instructions walk you through taking measurements according to current guidelines. The app can also remind you if you wish. These features are fully available in the free version as well. Get the free app now.