How much data does a speed test use?

The amount of data required by a speed test depends on the speed test used and on the internet speed you measure.

Research shows that, at least up to 200 Mbps, in most speed tests the amount of data used is directly proportional to the measured download speed.

Each speed test uses data to measure your internet speed. However, the differences in data use are large. A striking negative outlier is Ookla's speedtest. The Ookla speedtest often uses the most data to perform a speed test.

Of the accurate speed tests, Cloudflare and the Ookla Speedtest use a relatively large amount of data (at least for lower speeds). Google Fiber and TestMy.net, on the other hand, use relatively little data. While all these speed tests are approximately equally accurate.

Advice

If you want an accurate speed test that doesn't use a lot of data, use Google Fiber or TestMy.net.

The speed test that uses the least data by far is Internet Speed at a Glance.

Data use per speed test per measured speed

A meta-analysis of data from seven different tests (100 mbps, 200 mbps, WiFi-b, WiFi-g, WiFi-n, WiFi b-g-n and WiFi ac) shows that the amount of data needed for a speed test in most cases depends on the speed test used and the measured internet speed.

The graph below shows how much data is used in a speed test at different speeds for a number of speed tests.

Note that in the graph above is based on the average number of MB's (megabytes) used per Mbps (megabits per second).

Also note that we were able to do speed tests up to a download speed of 200 Mbps.

Some examples of measured values

The graph above gives only an indication based. In practice, other values will apply. For example, see the following purely measurement-based charts (note that the measured download data is in mebibytes (MiBs)).

This is because all measurements are done with the live option of vnstat, and vnstat gives the results in mebibytes.

M-Lab has a very consistent MiBs per Mbps ratio.

Ookla has a relatively constant MiBs per Mbps ratio.

Cloudflare's MiBs per Mbps ratio varies depending on the measured speed. Note that this data is based before Cloudflare stated that a speed test can consume up to 200 MB of data.

TestMy.net has a clear upper limit and hardly sends any data during the download test.

Remarkable findings

Note that these findings are based on our measurements where the max download speed is 200 Mbps. We know nothing about the data hunger of speed tests above 200 Mbps.

1. Internet Speed at a Glance clearly needs the least data to determine your download speed
2. Up to a download speed of 120 Mbps, Google Fiber and TestMy.net are the most accurate speed tests with the least data consumption
3. From a download speed of 120 Mbps, TestMy.net is the most accurate speed test with the least data consumption
4. Depending on the measured speed, the differences in the amount of data used between the speed tests can differ by a factor of 2.5 to 5
5. There appears to be (apart from Internet Speed at a Glance) an inverse correlation between the accuracy of the speed test and the amount of data used. Google Fiber, M-Lab and TestMy.net are very accurate speed tests but use relatively little data for a test
6. We found that there are eight speed tests that have an upper limit on the number of MBs downloaded. This includes the following speed tests:
   1. Internet Speed at a Glance with an upperlimit of roughly 0.05 MB
   2. TestMy.net with an upperlimit of roughly 100 MB
   3. Cloudflare with an upperlimit of 200 MB
   4. SpeedOf.me with an upperlimit of roughly 265 MB