How accurate are blood pressure monitors?

Do blood pressure monitors measure accurately?

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 inexpensive bargains starting at around 10 euros, but you can also spend triple-digit amounts.

That naturally raises the question of whether such a cheap device measures just as well as an expensive one. In short, it's not possible to say that directly. Unfortunately, we need to go into a little more detail.

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, the blood pressure of a certain number of people is measured. These measurements are compared with a measurement using the Korotkoff method, i.e. using a stethoscope. A test protocol defines how closely the values must match for the device to still be approved. The protocol also specifies the number of patients and which patients 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 subjects	33	85	>=85	96	>=85
Age	>=25	15-80	>12	>20	>12
Blood pressure range (SBP = systolic blood pressure, DBP = diastolic blood pressure)	SBP (mmHg): <130: 10-12 subjects, 130-160: 10-12, >160 mmHg: 10-12 DBP (mmHg): <80: 10-12, 80-100: 10-12, >100: 10-12	SBP (mmHg): <90: ≥8 subjects, 90-129: ≥20, 130-160: ≥20, 161-180: ≥20, >180: ≥8, DBP (mmHg): <60: ≥8 subjects, 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 subjects ≥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 and reference blood pressure of ≤ 5, 10, 15 mmHg Criteria for individual blood pressure measurements (Part 1) individual subjects (Part 2) Part 1: Passed if 73.7% (73/99) of the differences between measurements are ≤ 5 mmHg, 87.9% (87/99) are ≤ 10 mmHg, 97.6% (96/99) are ≤ 15 mmHg Part 2 (accuracy): Number of subjects with 0, 2 or 3 absolute differences ≤ 5 mmHg	Grading system (A, B, C, D) based on differences between paired measurements of ≤ 5, 10, 15 mmHg, separately for each observer and separately for SBP and DBP In addition, mean differences ≤ 5 mmHg and standard deviation ≤ 8 mmHg (AAMI recommendations)	Criteria based on mean blood pressure differences and their standard deviation criteria for individual blood pressure measurements and individual persons. Criteria 1 and 2 should be applied to SBP and DBP Criterion 1 (for individual blood pressure measurements): The mean blood pressure difference is ≤ 5 mmHg and the standard deviation is ≤ 8 mmHg Criterion 2 (for individual subjects): The mean difference and standard deviation of the blood pressure measurements are within the threshold defined by the mean of Criterion 1	Criteria based on the mean difference and standard deviation and the scoring system for individual paired SBP and DBP measurements Passed if the device meets all the following criteria: Mean difference for SBP and DBP ≤ 5 mmHg, standard deviation ≤ 8 mmHg, and score ≥ 55% of the maximum achievable score.	Criteria based on the mean blood pressure differences (test vs. reference) and their standard deviation criteria for individual blood pressure measurements and individual participants. Criteria 1 and 2 should be applied to SBP and DBP Criterion 1 (for individual blood pressure 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 standard deviation of the averaged blood pressure differences must be within a threshold defined by the mean from Criterion 1. In addition, the number of absolute blood pressure differences within 5, 10, and 15 mmHg (ESH-IP2) and standardized Bland-Altman scatter plots are presented. The mean test-reference blood pressure difference and the standard deviation for each cuff subgroup must be reported without pass/fail criteria for the test device

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

It is therefore not possible to say how accurate a device is. However, it is possible to say that it has passed a validation-that is, a test. Naturally, the more rigorous the validation, the better.
Some of the test protocols can also be viewed 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 individual measurements can be inaccurate, do not be alarmed by a single reading. Regular measurements are more important and also much more accurate, as they allow you to review all the readings together. For example, Tensana is useful for seeing changes over time in particular and taking appropriate action.

Download the app now and benefit from the clear layout.

This article is from Tensana – the leading app since 2011, helping hundreds of thousands of people 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 closely involved with high blood pressure since 2002 – initially because he was personally affected and, since 2009, as the developer of Tensana – and is now regarded as a recognized blood pressure expert thanks to his app and specialist platform, used millions of times, as well as his numerous publications. As the author of several health guides and specialist articles, he communicates complex knowledge in a clear and practical way.

We hope you found the article helpful. Accurate measurements are essential for good blood pressure control. Our app Tensana 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.