TL;DR
A really accurate speed test measures 100.8% of the advertised internet speed. This is due to safety margins taken (respectively +12% and -10%) when determining the internet speed.
Based on that knowledge and research, Cloudflare appears to be the most accurate speed test there is, assuming 201.6 Mbps is the correct value to measure. This speed test has by far the smallest deviation from the download speed to be measured,
Contents
Introduction
Progressive insight shows that two speeds can be regarded as the correct value. These speed are:
- the true internet speed
- the advertised internet speed
The true internet speed
The true internet speed is 12% higher than the advertised speed. During this speed test ISP offers a download speed of 200 Mbps. Hence the true internet speed is 224 Mbps.
As concluded earlier, only SpeedOf.me measures your true internet speed.
The advertised internet speed
With an advertised internet speed of 200 Mbps and the knowledge that speed tests like Ookla and Cloudflare measures 90% of the true internet speed, the "correct" speed to measure is 90% of 224 Mbps or more concrete 201.6 Mbps.
In this test, we examine which speed test is the most accurate, assuming 201.6 Mbps is the correct value to measure.
Method of measurement
For this test the download speed is measured five times per speed test.
Speed tests to test
For this test only the speed tests tested in the MB's used by a speed test test (at 200 Mbps) with the median between 200 and 206 Mbps are tested.
The measurements
- Astound 206.00, 206.00, 207.00, 206.00, 205.00 Mbps, median: 206.00 Mbps, standard deviation: 0.7 Mbps, average 206.0 Mbps, precision 0.40%
- Bredbandskollen 205.18, 205.21, 205.50, 205.45, 205.00 Mbps, median: 205.21 Mbps, standard deviation: 0.2 Mbps, average 205.3 Mbps, precision 0.17%
- Cloudflare 201, 201, 202, 201, 202 Mbps, median: 201 Mbps, standard deviation: 0.5 Mbps, average 201.4 Mbps, precision 0.48%
- DSLReports 204.3, 207.5, 202.4, 207.0, 201.1 Mbps, median: 204.3 Mbps, standard deviation: 2.8 Mbps, average 204.5 Mbps, precision 2.23%
- Fireprobe 204.57, 204.11, 203.84, 204.34, 204.01 Mbps, median: 204.11 Mbps, standard deviation: 0.3 Mbps, average 204.2 Mbps, precision 0.22%
- Google Fiber 203, 204, 203, 204, 202 Mbps, median: 203 Mbps, standard deviation: 0.8 Mbps, average 203.2 Mbps, precision 0.64%
- M-Lab 202.97, 202.97, 202.69, 201.83, 202.73 Mbps, median: 202.73 Mbps, standard deviation: 0.5 Mbps, average 202.6 Mbps, precision 0.32%
- Meter.net 199.7, 199.5, 200.5, 201.3, 196.8 Mbps, median: 199.7 Mbps, standard deviation: 1.7 Mbps, average 199.6 Mbps, precision 1.13%
- N Perf 205.2, 205.0, 205.4, 205.4, 205.4 Mbps, median: 205.4 Mbps, standard deviation: 0.2 Mbps, average 205.3 Mbps, precision 0.14%
- Ookla Speedtest 204.08, 203.84, 204.34, 200.55, 203.3 Mbps, median: 203.84 Mbps, standard deviation: 1.5 Mbps, average 203.2 Mbps, precision 1.07%
- SamKnows 203, 204, 204, 204, 204 Mbps, median: 204 Mbps, standard deviation: 0.4 Mbps, average 203.8 Mbps, precision 0.32%
- SpeedOf.me API Sample Page 222.6, 221.97, 221.93, 222.43, 222.68 Mbps, median: 222.43 Mbps, standard deviation: 0.4 Mbps, average 222.3 Mbps, precision 0.30%
- TestMy.net 203.4, 199.1, 200.1, 200.6, 200.9 Mbps, median: 200.6 Mbps, standard deviation: 1.6 Mbps, average 200.8 Mbps, precision 1.06%
- Xfinity xFi Speed Test 205.1, 205.3, 203.2, 204.4, 204.6 Mbps, median: 204.6 Mbps, standard deviation: 0.8 Mbps, average 204.5 Mbps, precision 0.58%
Conclusions
Based on the measurements above it can be concluded that based on the average of the measurements Cloudflare is most accurate with a bias of -0.2 Mbps and a precision of 0.48%.
The top 5 of accurate speed tests
Based on the absolute bias based on the average of the measurements this is the top 5 of most accurate speed tests (when the advertised internet speed is 200 Mbps):