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Cell Signal Strength

What do the signal bars mean?

Signal bars on a cell phone are usually not an accurate measurement of cell phone signal strength. Bars are like a gas gauge: They tell you the general range but not the actual amount of signal you're receiving. Two different brands of cell phones, using the same carrier, placed next to each other, might show different numbers of bars.

Some carriers brag that they have "more bars" in more locations than their competitors. When your carrier knows you have enough signal to make a call and talk, bars can be displayed any way they want and you won't know the difference.

Take a look at the notification bar at the top my Samsung Note 5 screen: The signal indicator says I have 4 bars (circled in red). To most people that says "very good signal." But is it, actually?

Android smartphone screen with signal strength bars circled

How is signal strength actually measured?

The signal your phone receives from a cell tower is measured in decibel-milliwatts (dBm), a unit of electrical power in decibels (dB), referenced to 1 milliwatt (mW). There are three things you need to know to understand how decibel-milliwatts work:

  1. One milliwatt of power is equal to 0 dBm. Since cellular signal operates on less power than that (as low as 0.0000000001 mW, sometimes less), dBm signal strength is measured in negative numbers. The closer you get to 0 dBm, the stronger the signal; so, −70 dBm is stronger than −90 dBm.
  2. The milliwatt scale is logarithmic , meaning that a change in dBm yields an exponential change in mW. For example, −70 dBm (0.0000001 mW) is ten times more powerful than −80 dBm (0.00000001 mW), one hundred times more powerful than −90 dBm (0.000000001 mW), and one thousand times more powerful than −100 dbM (0.0000000001 mW).
  3. Any change in dbm (gain or loss ) is noted in ±dB. So if you start with −90 dBm of cellular signal, and you install a cell phone signal booster system that gives you +30 dB of gain, you'll end up with −60 dBm of signal.

So, what is considered strong or weak cell signal?

Power level (dBm)
Signal strength
Greater than −60
Excellent (you're very close to a cell tower)
−60 to −75
Very good (usually this is the best it gets)
−76 to −90
Good (you're in an area with decent coverage)
−91 to −100
Fair (coverage is spotty, and may be slow)
−100 to −110
Poor (very weak; you may be having connectivity problems)
Less than −110 dBm
No signal (you're probably unable to make or complete a call)

So what's my actual cell signal strength?

Most smartphones can display the cell signal dBm reading. Using this number is much more accurate than looking at "bars."

Android

  • Stock Android phones (like the Nexus and Moto X): Go to Settings (the "gear" icon), tap About phone , tap Status , then tap SIM status. Under Signal strength , you'll see your signal in dBm (circled in red, below):
    Signal strength reading on a stock Android phone

    (Notice how the phone above is receiving −95 dBm of signal, which is "fair," even though the number of bars at the top—circled in blue—is supposedly showing full strength!)

  • Samsung Android phones: Go to Settings (the "gear" icon), tap About Phone , then tap Status. Look under Signal strength:
    Signal strength reading on a Samsung Android phone
  • Other Android phones may show signal strength in a different location under the Settings > About phone menu.

iPhone

To see the signal strength reading on an iPhone, follow these steps:

  1. Dial 3001#12345# and hit the Call button:
    Dial *3001#12345#* to put an iPhone into Field Test Mode

    This will put your iPhone into Field Test Mode :

    iPhone in Field Test Mode
  2. Once you're in Field Test Mode, press and hold the Power button on the side of the phone until the "Slide to Power Off" message appears, then release the power button.
  3. Press and hold the Home button until the Home screen appears.

    The bars or dots at the left side of Status bar at the top of the screen will be replaced by a number showing the iPhone's received signal strength in dBm:

iPhone with dBm displayed in the Status bar

This change is permanent until you reverse it. To return your display to bars or dots, repeat step 1 (above); once you're in Field Test Mode, tap Back to Phone at the top of the screen, and your phone will be back in its original display state.

Cell signal will fluctuate

The signal strength you receive from a cell tower will increase and decrease, even if you aren't moving. At rest, you'll frequently see fluctuations around ±5 dBm. The fluctuation is primarily caused by two factors:

  1. The main cause is user load on the cell tower: The more people connected to one tower, the weaker the signal. Peak usage times (rush hour, lunch hour, etc.) will result in lower power for all users.
  2. Smartphones, with their ability to download and stream data, can also put considerable load on a tower.

Because of shifting usage loads, signal strength from a cell tower to your phone is constantly changing. If your cell signal is −95 dBm, you can usually make a call without any problems. If your −95 dBm signal fluctuates down to −100 dBm because of the load on the tower, you might drop the call for a moment, but be able to redial and resume in a few seconds.

Physical barriers block cell signals

You can be close to a cell tower, but still have a weak cell signal. Many building materials—including concrete, metal, low-e glass, wood, and plaster—will reduce or block cell signal from entering into a building and reaching your phone. Stucco with wire mesh, metal roofs, large logs, and vapor barriers in attics also impede cell signals, resulting in weak cellular reception.

Even if you're outdoors, dense forest, bluffs, and hills will reduce or block cell signals. Low areas around lakes, rivers, and gullies can have problems—there is a signal, but passing way over your head.

Dense urban areas with tall buildings have a different set of problems: Sometimes the top floors of buildings, 40–50 stories up, can't get a good cell signal because towers are broadcasting at a lower elevation.

I can see the tower, but I have no signal

Sometimes you can see your carrier's tower down the road or off in the distance, but you still have weak cell signal. Just because you can see the tower does not mean that the tower is broadcasting in your direction. This type of issue is more common along remote highways where cell signal broadcast is mostly concentrated toward the highway and hardly at all behind the tower.

Directional sector antennas used on cell towers broadcast the broadcast of signal only in certain directions. Just because you can see the tower does not mean that it sees you.

It's also possible that the tower nearest you is operating for a different carrier than the one you're using.

Frequency and technology limitations

Different frequencies carry different distances. Carriers that use the 800 MHz frequency range can broadcast their signals more than twice the distance of carriers that use 1900 MHz frequencies. There are only so many FCC licenses available for each band of frequencies, and when they are all claimed, carriers have to use other frequencies. 800 MHz also has better penetration capabilities than 1900 MHz, so cell signals in buildings may be stronger with 800 MHz. If you can find out which frequency your carrier uses in your area, you might be able to discover the reason behind reception issues you're having.

Another factor is the channel-access technology: Some carriers use the GSM ( Global System for Mobile communications ) protocol, while other use CDMA (Code Division Multiple Access ). CDMA broadcasts farther than GSM. In the United States, Verizon, Sprint, U.S. Cellular use CDMA, while AT&T and T-Mobile are GSM carriers; in Canada, Bell, Telus, and SasTel are CDMA carriers; Rogers, Fido, and Wind use GSM. (This, by the way, explains why you can't take your Verizon phone and activate it on AT&T's network: Every cell phone has a radio that works either on GSM or CDMA, but not both…usually.)

Smartphone apps that display your cell signal strength

These apps will display your cell phone signal strength and other details about your connection.

These links to third-party software are provided "as is" without warranty of any kind, either expressed or implied, and such software is to be used at your own risk. Powerful Signal will not be liable for any damages that you may suffer in connection with downloading, installing, or using such software.

Android apps from the Google Play Store

iPhone apps from the App Store

Call Powerful Signal at 866-912-3444

The representatives at Powerful Signal can help you determine why your cell phone signal may not be as strong as you need it, and can help you find a solution to your problem.

Learn more about cell signal strength from WilsonPro:

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