Actually, this five scale system is mainly subjective. Five by five means that signal strength is good and that the message is easily intelligible. One by five means that the signal is very weak, but that the message is intelligible. Five by one means that the signal is strong, but the message is garbled.

It's an old traditional method used for radio in airplanes, and perhaps also ships. But there's nothing very precise implied.

What the mobile receiver measures is the signal power, which might be in the range of -70 dBm to -120 dBm (or something like that). The software then maps this measurement to bars. -70 dBm is a very strong signal so it probably gives 5 bars, while -120 dBm might be weak enough for 1 bar.

If you have an iPhone, you can enter the hidden Field Test Mode and get all the details that the phone has access to: http://www.ubersignal.com/field-test-mode

What do the signal bars on your smartphone actually mean?

5-bar phone signal: What's it get you?

Dear, check this link::

http://www.digitaltrends.com/mobile/what-do-the-bars-on-your-smartphone-mean-we-asked-an-expert/

http://www.cnet.com/au/news/5-bar-phone-signal-whats-it-get-you-faq/

Yes, but those bars on your smartphone are not the "five by five" convention. They only represent a non-precise level of signal strength, from weak to strong. I think we are mixing apples and oranges.

http://www.askacfi.com/694/what-is-meant-by-five-by-five.htm

http://www.urbandictionary.com/define.php?term=5%20by%205

In all cases, the numbers do not represent anything quantitative, such as dBm or SNR.

Note this other, 3-digit standard, used by ham radio operators:

http://www.acsu.buffalo.edu/~maxwell/RSTInfo.html

Well, the main issue is that there is no convention. But in a given phone, it will measure some quantity and use a set of thresholds to decide how many bars to show. The measurement is probably the dBm received signal level that the phone is measuring at regular intervals.

If the expected result is to be used for a research-based test, do not rely on "five by five" indicators since it may miss out on values in between. But it depends on the manufacturer's configuration, it is still an indicator and not a value.

Thank you all for your contribution

Maybe it is not the focus of the question but I would add that 5 bars status does not mean necessarily that you will get a good service or higher data rates. The main reason is that the bars display indicates received power and not SINR (Signal to Interference plus Noise Ratio) or SIR (Signal to Interference Ratio).

Dear Francisco Rafael Marques Lima,

I was just wondering how one could reliably use the method for signal measurements. I agree with you that SINR is not measured and therefore, the bars would indicate good service.

For indoors measurement, I think that indication is very reliable and can serve as a true SNR.