How Do Internet Speed Tests Work?

Have you ever wondered how Internet speed tests work? And why you get different results from different websites? We have too. Here’s what we dug up.

Internet speeds are exponentially increasing year after year – the Internet we surf today is a heck of a lot faster than it was in 2011. At some point, when boredom has well and truly set in on an idle Tuesday, it’s only natural that you might want to know where your own Internet connection clocks in on the speed spectrum. But if you were to check on one website and then again on another, you might and probably will see some discrepancy.

That was certainly our experience. We used and got the following results:

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Five minutes later we opted for and were presented with these conflicting stats:

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What gives?

Firstly it’s worth understanding how the speed tests actually work. Most of them give you an upload and a download speed, which they calculate by sending sample binary files to your computer with instructions to send them back again. Some services like along with Comcast and other ISPs provide a “ping” result alongside download and upload speeds. This is basically a measure of latency, which is estimated by sending HTTP requests to the speed test’s server and measuring how long it takes for a response. uses these results to conduct what they call the “real test” – now they have a rough idea of how speedy your Internet connection is, they can saturate the line to get a more accurate measurement of the maximum amount of data you can download in 10 seconds, whilst making sure it doesn’t take forever and a day to complete the test.

By and large that’s how most online speed tests get their results, so what causes the inconsistency?

There are a number of factors that can impact the accuracy of a reading.

Tests are basic!

Firstly, the test is conducted with sample files, which differ substantially from what you might typically use the web for – streaming that episode of True Detective on HBO Go places a higher burden on your modem.

Location, location, location

The tests involve sending and receiving information between your computer and the test giver’s server. Where that server may be will change the reading considerably – you’ll get a much faster reading if the server is in the same town or nearby than you would if it was the next state over. Most test services will automatically select the server closest to your location, others will allow you to select the server’s location, which will give you an idea of the difference that distance makes.

What else are you doing online?

What else do you have active on your Wi-Fi connected devices? Are you still watching Matthew McConaughey on your iPad while you’re testing your connection speed on a laptop? That’ll make a big difference; so if you want to get the most accurate estimation possible, close any other applications that might compete for bandwidth.

Rush hour versus downtime

The same principle applies to the wider network: if there are more people online in your local area then it’s likely that will result in a slightly slower speed. Peak time Internet is not as fast as it would be at 3 a.m.