How reliable are Internet Speed Test and why do speed results differ?

How reliable are Internet Speed Test and why do speed results differ?

Checking our internet speed is one of the first ways we diagnose our internet speed issues and when we see those terrible results that is when we see red and get on the phone to our ISP! But how accurate are speed testing websites like and Are they reliable enough that you can use those test results to call your ISP to complain about your Internet speed?

Yes and No.

We are all familiar with the situation. You would be streaming a movie and it starts to buffer or you are in the middle of a playing a game and it starts to lag badly. What do you do? The first thing you do is look at your internet connection – are you still connected to the WiFi or the LAN?

You then open a random website and see if that loads. It does, but it seems slow and sluggish – so the next step is to run a speed test on a website such as or before calling the ISP customer service.

Your ISP checks your line telling you its all fine and even asks you to run another speed test which magically proves that the line speed is fine.

How is that possible? How can you run speed tests on different sites they show different results. If it is really measuring the speed then should they not all be the same?

Why do speed tests show different results?

When you run a speed test, the system tests three things: your download speed, your upload speed, and your latency. Each one of these is important and you can watch this video to determine how much internet speed you actually need:

The speed testing sites are able to measure the upload, download, and ping by using their algorithm which determines HOW to best test your speed. Without all the technical gumf, speed test sites roughly work like this:

  1. The system would start by looking up your IP address to get your approximate location.
  2. It then finds some of its testing servers that are closest to you.
  3. Once that is done, a test is run to determine which is the closest server to you not based on distance but on a ping test result. The faster the result, the more accurate the testing results will be.

The test is run and results are displayed.

Why do test sites show different speed results?

This is because of 3 variables:

  1. When you run a speed test, you initiate it from your device be it a computer or a phone) or a tablet. The test instruction is run via your home network, then onto your router to the ISP and finally out onto the internet. While you are testing your speed, your network is actively serving all the devices in your house. Therefore, you will get different results if it’s just you on the network versus if the entire family is on the network streaming/ backing up to the cloud/ downloading game updates on the PS4.
  2. Your ISP could be shaping or throttling your bandwidth. This means that they give priority to some traffic like web browsing, but lower priority to things like games. Here is how you test if your ISP is throttling your bandwidth.
  3. Each speed test site calculates their speed based on its own algorithm. These could include elements such as server load, number of connections at the time of testing, architecture, network distance, size of data to upload/ download, and more. Therefore no two testing sites are going to provide the same results. This image is from showing some of their architecture.

Speed test fast architecture - thetechieguy

Are Speed Tests sites unreliable?

Not at all. you just need to use the speed test sites as a barometer and not an exact science. In other words, these tests are an indicator of your speed and not an exact figure. Before you call your ISP, you should run the test several times in order to ascertain an average upload, average download, and averages ping speeds. [Notes to the geeks: Now you can get really geeky and flush your DNS in between test, get a new IP address from ISP, but I suspect if you are doing that, you are reading this]

You should also test multiple sites to get an idea across various testing sites so that you have some data to work with. It’s not perfect, but it’s good enough.

Most people will not get the exact speed they are paying for so don’t panic when you don’t see that. However, you should aim to get about 70% or 80% of that speed. Anything below that, I would not be happy and would be calling my ISP to check my lines!


Liron Segev - TheTechieGuy

Liron Segev is an award-winning tech blogger, YouTube strategist, and Podcaster. He helps brands tell their stories in an engaging way that non-techies can relate to. He also drinks way too much coffee! @Liron_Segev on Twitter