My wifi signal is within the range around -25 to -35 dBm base on the meter reading is it good or bad?

What is the worst (lowest) and the best (maximum) of WiFi signal measured in dBm?

and why is it measured in negative value?

 

It is actually pretty good.

dBm is a measurement with respect to a power level of 1 milliwatt or 0.001 watts. A positive dBm value would represent a power greater than one milliwatt, and a negative dBm value represents a power level smaller than 1 milliwatt.

\(-25\;\text dBm \;=\;10\times\math log(\frac{P}{.001})\)
\(-2.5\;=\; \math log(\frac{P}{.001})\)
\(10^{-2.5}\;=\;\frac{P}{.001}\)
\(3.1623\;\times\;10^{-3}\;=\;\frac{P}{.001}\)
\(3.1623\;\times\;10^{-6}\;=\;\text P\;\approx\; 3.2 \mu \text watts\)

\(-35\;\text dBm \;=\;10\times\math log(\frac{P}{.001})\)
\(-3.5\;=\; \math log(\frac{P}{.001})\)
\(10^{-3.5}\;=\;\frac{P}{.001}\)
\(316.23\;\times\;10^{-6}\;=\;\frac{P}{.001}\)
\(316.23\;\times\;10^{-9}\;=\;\text P\;\approx\; .32 \mu \text watts\)

Typical minimums for a modern receiver are -125 to -135 dBm so you are several orders of magnitude above the minimum receiver threshold.

 

dB is the logarithmic ratio of two powers (dB= 10*log(P1/P2).
For dBm a value of 1 mW is used for P2.
So a negative dB simply means that the P1 value you are measuring is less than 1 mW.
Thus -25dBm represents a power of ≈3.2μW.

Where are you measuring this -25 to -35dBm?
This value will vary depending upon how far you are from the WiFi modem.

 

dB is the logarithmic ratio of two powers (dB= 10*log(P1/P2).
For dBm a value of 1 mW is used for P2.
So a negative dB simply means that the P1 value you are measuring is less than 1 mW.
Thus -25dBm represents a power of ≈3.2μW.

Where are you measuring this -25 to -35dBm?
This value will vary depending upon how far you are from the WiFi modem.

the wifi modem just next to my phone

 

the wifi modem just next to my phone

Any value over -60dbm to -80dbm is medium signal, anything between -40 to -60 is excellent, download Wifi analyser on Android by Farproc.

Lower is strongest.

 

Highly recommend to try the WiFi analyzer . With the help of the application, you can quickly and efficiently find and eliminate the cause of a bad signal. An intuitive interface will save your time. First check your network to be sure that the source of the problem not in the hardware part, after you can try to reinstall your smartphone software or try to visit service center.