The short answer is: a download measurement with Bredbandskollen is running between 4 and 10 seconds depending on the stability of the connection you are measuring on. If the connection is unstable then Bredbandskollen needs more time to determine the speed. If that is the case, we measure download the full 10 seconds and the amount of MB data used will be about the same as the result speed. This means that if the the download speed is 20 Mbit/s, then 20 MB is consumed out of your data plan.
If you on the other hand have a more stable connection, Bredbandskollen will only need about half the time to determine the speed which will have a direct effect on the amount of data used. The upload measurement is also consuming data. But since this speed usually is much slower, the amount of data used is also much less. The total amount of data used is always displayed in the app after a completed measurement.
The long answer is: when Bredbandskollen measures, it will send data to and from our servers as fast as it can. This is how many apps in your phone work, such as your web browser, for instance. The total measurement runs between 10 to 30 seconds. During this time, three different measurements are taking place. The first measurement consumes very little data and only measures the response time.
Then the download measurement starts (receiving files) which also takes between 4 to 10 seconds. During this time we try to download data as fast as possible. The same applies to the following upload measurement (sending files). This part also takes between 4 to 10 seconds but here we will try to send as much data as possible instead. If the connection is less stable, Bredbandskollen needs more time to determine the speed (up to 10 seconds). If it’s more stable on the other hand, we need less (down to 4 seconds).
The amount of data consumed depends on how fast your connection is during the measurement. If you have a phone that only supports the early 3g networks or if you find yourself in a place with poor coverage resulting in an unstable connection (10 seconds used) resulting in a speed of about 5 Mbits down and 0.5 Mbits up, your total used data amounts to: ((5/8) + (0,5/8)) x 10 = 6.87 MB.
If your connection is really stable and presents the same result, the amount of data used from your plan will only amount to ((5/8) + (0,5/8))x4 = 2,75 MB.
On the other hand if you find yourself in a place with a fast 4g network, have a 4g phone on an unstable connection and get a result of about 50 Mbps down and 5 Mbps up, your total amount of data consumed can be significantly higher: ((50/8) + (5/8)) x 10 = 68.75 MB.
Most of your measurements will probably resemble the first example and more seldom the second one, but the faster your mobile network becomes, the quicker you can do things on the Internet. But since the Bredbandskollens app uses a maximum period of 10 seconds to download data, more data is transfered the faster the connection is at your location.
To give you some perspective on the amount of data used you could compare the first measurement (5 MB) to loading a ordinary news web landing page.
If your operator supports IPV6, the app will perform a second measurement over this protocol every time you start a measurement. This means each measurement will use up twice as much data from your plan.
Please note that if you use the map in the app, this will also consume data. Measurements done when you are connected via a wireless network at home or at work are not eating away at your data plan since this traffic will not pass the network of your mobile operator.
Your operator has probably set a limit to the amount of data you can use per month. In case you would exceed this data plan it is not uncommon for the operator to lower your speed until the end of month. Usually, the speed is restored at the beginning of the following month and you can surf as usual again.
Sweden's mobile phone operators have worked hard in recent years to make our mobile networks faster and better. On the other hand, the conditions for users has not improved at the same pace. Data caps of 0.5 GB or 2 GB are not uncommon which means that it becomes harder and harder for a user to freely use their phone without hitting the ceiling. The Bredbandskollen app is an example of an app that suffers from this. A few measurement per day on a fast connection could consume a large portion of your data cap.