## TL;DR

The most accurate speed test depends on the speed you measure. M-Lab is the only speed test that appears in the top 3 of most accurate speed tests for every speed tested.

## When is a speed test accurate?

At Course Hero it is stated that:

Science is based on observation and experiment—that is, on measurements. Accuracy is how close a measurement is to the correct value for that measurement.

The picture below of Wikipedia Commons makes clear that there is a difference between accuracy and precision.

Preferably, a speed test is accurate and of high precision.

However, the starting point for determining an accurate speed test is that you need to know the correct value. So the question is, what is the correct value to measure?

## The correct value to measure

Progressive insight shows that a mainstream speed test should measure 100.8% of the advertised internet speed.

Based on a meta-analysis of hundreds of test results, the following can be concluded:

### The best speed test at 50 Mbps

With an advertised speed of 50 Mbps, the following speed tests are most accurate:

- M-Lab, accuracy 0.0 Mbps, standard error 0.9 Mbps
- Fireprobe®, accuracy 0.0 Mbps, standard error 1.1 Mbps
- Ookla Speedtest, accuracy 0.1 Mbps, standard error 0.9 Mbps

### The best speed test at 75 Mbps

With an advertised speed of 75 Mbps, the following speed tests are most accurate:

- DSLReports, accuracy 0.1 Mbps, standard error 1.0 Mbps
- M-Lab, accuracy 0.5 Mbps, standard error 0.2 Mbps
- Ookla Speedtest, accuracy 0.5 Mbps, standard error 1.1 Mbps

### The best speed test at 100 Mbps

With an advertised speed of 100 Mbps, the following speed tests are most accurate:

- Cloudflare, accuracy 0.0 Mbps, standard error 0.5 Mbps
- M-Lab, accuracy 0.3 Mbps, standard error 1.2 Mbps
- TestMy.net, accuracy 0.3 Mbps, standard error 1.0 Mbps

### The best speed test at 200 Mbps

With an advertised speed of 200 Mbps, the following speed tests are most accurate:

- Cloudflare, accuracy 0.0 Mbps, standard error 0.6 Mbps
- TestMy.net, accuracy 0.2 Mbps, standard error 1.0 Mbps
- M-Lab, accuracy 0.4 Mbps, standard error 1.6 Mbps

## Earlier conclusions

Below you can read the earlier conclusions made regarding the accuracy of speed tests.

### Findings of an earlier meta-analysis

Based on that knowledge all previous relevant test results have been reanalyzed.

Speed tests with an accuracy of max 1% are considered as accurate. Sorting this speed tests on the precision (or better said the standard error) gives the following top 5 of accurate speed tests:

- Google Fiber Accuracy: 1.0%, Standard error: 0.11 Mbps
- M-Lab Accuracy: 0.4%, Standard error: 0.18 Mbps
- Fireprobe® Accuracy: 0.7%, Standard error: 0.23 Mbps
- Ookla Speedtest Accuracy: 0.1%, Standard error: 0.25 Mbps
- DSLReports Accuracy: 0.4%, Standard error: 0.37 Mbps

### The correct value to measure (again)

When you measure the internet speed with different speed tests, you get different results. The graph below shows this clearly. This chart is based on the measurements taken as part of the ultimate speed test test 2022 (Advertised speed is 75 Mbps).

The graph above has the same pattern as the graph below which was created in 2020 (Advertised speed is 50 Mbps). Based on this graph it was concluded in 2020 that there are three categories of speed tests.

The tested speed tests for the ultimate speed test test are classified into the following categories:

- Realistic
- Mainstream
- Conservative

### Two correct values to measure?

Based on the findings above there are values which might be considered as the correct value: the advertised speed and the actual speed.

The correct value and therefore also the accuracy depends on what you expect a speed test to measure: the advertised speed or the actual speed.

## Crossing out inaccurate speed tests

A seemingly easy way to find an accurate speed test is to cross out inaccurate speed tests.

To do this, a speed test is considered inaccurate if:

- The speed test gives no result
- The median is low, that is the median is less than the adverstised speed (75 Mbps)
- The median is doubtful, that is the median is somewhere between the advertised and the actual speed (between 77 and 82 Mbps)
- The speed test has an unintended large standard deviation, that is the standard deviation is larger than 2 Mbps

Based on these criteria the following venn diagram has been made.

### A long list of accurate speed tests

By crossing out 16 of the 27 speed tests, the following 11 speed tests could be considered as accurate:

- Broadband Speed Checker
- Cloudflare
- DSLReports
- Fireprobe
- Google Fiber
- Internet Speed at a Glance
- M-Lab
- Ookla Speed Test
- SamKnows
- SpeedOf.me
- SpeedSmart

Most of these speed tests are mainstream speed tests. The exceptions are:

- Internet Speed at a Glance which is considered as realistic and conservative
- SpeedOf.me

## The most accurate speed test to measure the advertised speed

In the speed test test of 2022, speed tests with a median between 72 and 78 Mbps were considered a mainstream speed test. These speed tests measure the advertised speed. In the graph below we zoom in on this category. Based on this graph it is hard to conclude which speed test is most accurate. Frankly, there are several possible considerations.

### Consideration 1, Cloudflare is most accurate

Cloudflare's median is closest to the advertised speed (the 75 Mbps line in the graph above), hence Cloudflare is the most accurate speed test although the standard deviation is relative high.

### Consideration 2, SpeedSmart is most accurate (although wrong), with a small standard deviation

Because SpeedSmart's range does not reach the 75 Mbps line, this speed test always indicates too high a value. However, SpeedSmart has such a small standard deviation that the final measurement result is always relatively close to but always above the actual value. Although it is always wrong, you could argue that SpeedSmart is the most accurate speed test.

### Consideration 3, Google Fiber is the overall best (although wrong)

When you accept wrong results (consideration 2) and realise that Cloudflare has an overlap in scope with eleven other speed tests. Scientifically, this means that these speed tests are just as good as Cloudflare.

Accuracy alone is clearly not distinctive enough to rate these 12 speed tests. Therefore, the 2022 speed test test examined which mainstream speed test is the best. Various criteria were used for this study. The conclusion of this research is that Google Fiber has the best overall score.

## The most accurate speed test to measure the actual speed

The speed test test of 2021 was a relative short test to find out which speed test has the lowest bias in relation to the actual delivered download speed (84 Mbps in 2021).

### Consideration 4, SpeedOf.me (max) is most accurate

At the time, the conclusion was that the maximum speed as stated by SpeedOf.me most accurately measures the actual internet speed.

Based on the graph below, you can safely assume that this is still the case.

### Consideration 5, Internet Speed at a Glance is the best

Of the 2 speed tests crossing the 84 Mbps line only Internet Speed at a Glance is a recommended speed test. Hence Internet Speed at a Glance is the best speed test there is.

## The top 5 of accurate speed tests

The considerations mentioned above results in the following top 5 of accurate speed tests: