Thunderbolt Electronics' Blog: November 2015

What do the bars on your mobile phone mean? As it turns out, next to nothing!

We know what the bars graphic on the home screen of our mobile phone is supposed to mean. Signal strength, right? How strong the signal is that your phone is receiving right now?

In a very general sense, that is what the bars (or dots, depending on your phone model) do. They generally indicate the relative strength of the available signal.

The key word here is ‘relative.’

If your mobile phone displays from one to five bars (dots) indicating signal strength, then a display of four bars indicates a stronger available signal than three bars, and three a stronger signal than two, etc.

But this is all your phone’s bars (dots) graphic can tell you.

You do not know by observing the bars graphic how strong the available signal actually is, nor how much stronger a four-bar signal is than a three-bar signal, etc.

You may have had this experience – your phone shows four bars, but when you try to text or download you can’t do it because you have no service despite the four big bars you see.

There are no standards for signal strength bars.

Every mobile phone manufacturer uses an algorithm they have developed to sense the strength level of available signal. And then they show you however many or few bars they choose.

It is impossible to compare signal strength bars between different phone models.

The most reliable way to determine how strong a signal is for your phone is to take a reading in decibels, or dBm. Decibels is used in radio, microwave and fiber optic networks as a convenient measure of absolute power because of its capability to express both very large and very small values in a short form.

dBm is typically expressed as a negative number, -88 for example. The closer to zero the reading is, the stronger the cell phone signal. So for example, -79 dBm is a stronger signal than -88 dBm.

A reading of -50 is the strongest signal you will see. When a signal is weaker than -100 dBm, that’s a pretty weak signal. If the signal gets much weaker than that, you likely won’t have service.

dBm reading on most Android phones and iPhone 5 and newer models. This is the only way to know how strong your available cell signal really is.
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